bluuebunny/crossref_metadata_2025 huggingface dataset:
Lead isotopes and selected metals in ice from Law Dome, Antarctica
Authors: Rosman K.J. R. , Chisiiolm W. , Boutron C. F. , Hong S. , Edwards R. , Morgan Vin , Sedwick P. N.
Published: November 2017

The isotopic composition of Pb and the concentrations of Pb, Ba and Bi wert-
measured in selected ice-core samples from Law Dome, East Antarctica, to a depth
of 1196 m. The range of concentrat ions found in decontaminated ice was 0.03-1.5
pgg−1 for Pb, 0.9-6.1 pgg−1 for Ba
and 0.4 17 fgg −1 for Bi, excluding the deepest sample which
contained ~1 pjpm of rock dust. The abundances of all four stable lead isotopes
were measured and gave 206Pb/207Pb
ratios up to ~1.23. Avalue of
208Pb/207Pb= 2.78 was measured in the
deepest sample and is consistent with reported Pb isotope ratios of Antarctic
gran-ulites. Although the element concentrations in some samples were lower than
have been reported elsewhere, geochemkal and isotopic evidence indicated that a
number of samples were contaminated with Pb not present in the original ice.
However, it appears that the technical skills now available are approaching the
level where careful sample selection, decontamination and analysis can yield
accurate results for the concentration and isotopic composition of Pb in Earth's
purest naturally occurring ice.
Spatial variability of snow chemistry in western Dronning Maud Land,
Antarctica
Authors: Stenbrrg Malin , Isaksson Elisabeth , Hansson Margareta , Karlen WibjöRn , Mayewski Paul A. , Twickler Mark S. , Whitlow Sallie I. , Gundestrup Niels
Published: November 2017

During the austral summer of 1993-94 a number of 1-2 m deep snow pits were
sampled in connection with firn-coring in western Dronning Maud Land, Antarctica.
The traverse went from 800 to about 3000 m a.s.l. upon the high-altitude plateau.
Profiles of cations (Na+, K+,
Mg2+, Ca2+), anions
(Cl−, NO3-, SO4
2- , CH3SO3
−) and stable oxygen isotopes (δ18O)
from 11 snow pils are presented here. Close to the coast 2 m of snow accumulates
in about 2-3 years, whilst at sites on the high-altitude plateau 2 m of snow
accumulates in 10—14 years. The spatial variation in ion concentrations shows that
the ions can be divided into two groups, one with sea-salt elements and methane
sulfonate and the other with nitrate and sulfate. For the sca-salt elements and
methane sulfonate the concentrations decrease with increasing altitude and
increasing distance from the coast, as well as with decreasing temperature and
decreasing accumulation rate. For nitrate and sulfate the concentrations are
constant or increase with respect to these parameters. This pattern suggests that
the sources for sca-salt elements and methane sulfonate are local, whereas the
sources for nitrate and sulfate are a mixture of local and long-range
transport.
Relationships between Antarctic sea-ice concentration, wind stress and
temperature temporal variability, and their changes with distance from the
coast
Authors: Watkins Andrew B. , Simmonds Ian
Published: November 2017

Daily A ntarrtir sea-ice concentration, wind and temperature data for the
years 1988-94 were analyzed using Fourier techniques to determine their temporal
spectra for three equal-length “seasons". The percentage of the total variance
explained (VE) by each individual wave (i.e. frequency] was calculated, and
spatial averages made over six latitudinal hands surrounding Antarctica.
Comparisons of trie sea-ice concentration, wind stress and surface air-temperature
spectra showed sea-ice concentration VE has smallest, and wind-stress VE greatest,
value in the synoptic time-scales. Conversely, in the 20-25 day window the
wind-stress VE is smallest, and sea-ice concentration VE greatest. This “red
shift” of the sea-ice concentration suggests it has inertia to the wind slress and
temperature Forcing. Resulls show the magnitude of the red shift varies with not
only time of year, but also distance from the coast, and is dependent upon the
position of the Antarctic circumpolar trough.
Modelling global warming and Antarctic sea-ice changes over the past century
Authors: Wu Xingren , Budd W.F.
Published: November 2017

An atmosphere–sea-ice model is used in combination with results from a coupled atmosphere–ocean–sea-ice model to examine the changes of the Antarctic sea-ice cover influenced by atmospheric circulation associated with the global sea-surface temperature (SST) changes alone over the past century. Using the current climatological SST of Reynolds for forcing, a reasonable seasonal simulation of the Antarctic sea-ice cover for the present climate (including ice concentration, thickness and coverage) is obtained. When global SST anomalies for the past century (derived from the coupled atmosphere–ocean–sea-ice model) are imposed, sea ice becomes more extensive, on the annual average, by 0.7-1.2° of latitude, more compact by about 5-7%, and thicker by 7-13 cm, than at present. These changes are similar to those simulated from changes in greenhouse gases using the coupled atmosphere–ocean–sea-ice model which gave corresponding changes of about 0.8° of latitude in extent, 6% in ice concentration and 12 cm in ice thickness. The simulated change in annual mean global surface temperature by the coupled atmosphere–ocean–sea-ice model was 0.7 Κ (0.6 Κ over the ocean including sea ice) which is similar to the observed change. Over the Antarctic the corresponding simulated change is 1.2 Κ which also appears compatible with observations.
Velocities of Thwaites Glacier and smaller glaciers along the Marie Byrd Land
coast, West Antarctica
Authors: Rosanova C. E. , Lucchitta B. K. , Ferrigno J. G.
Published: November 2017

Average velocities for time intervals ranging from < 1 to 15 years
were measured by tracking ice-surface patterns on sequential Landsat and European
Remote-sensing Satellite synthetic aperture radar images. Velocities ofThwaites
Glacier range from 2.2 km a−1 above the grounding line to 3.4
km a−1 at the limit of measurements onThwaites Glacier ice
tongue. The glacier increases in velocity by about 1 km a−1
where it crosses the grounding line. Over the period 1984-93, Thwaites Glacier ice
tongue accelerated by about 0.6 kin a .Velocities of the floating part of several
minor glaciers and some ice shelves are also determined: Land Glacier, 17—1.9 km
a−1 ; DeVicq Glacier, 0.7-1.1 km a−1;
Dotson Ice Shelf 0.2-0.5 km a−1; Gctz Ice Shelf, 0.2-0.8 km
a−1; and Sulzberger Ice Shelf, 0.01 -0.02 km
a−1. The high velocities along the Marie Byrd Land coast
are consistent with the high precipitation rates over West Antarctica and, for
some of the glaciers, the lack of buttressing ice shelves.
Evaluation of a regional atmospheric model for January 1993, using in situ
measurements from the Antarctic
Authors: Van Lipzig Nicole P. M. , Van Meijgaard Erik , Oerlemans Johannes
Published: November 2017

The performance of a regional atmospheric climate model (RACMO) with a
horizontal resolution of 55 km X 55 km is evaluated using measured temperature and
humidity profiles. Parameterisations of the physical processes are taken from the
EC-HAM4 general circulation model (GCM). Sea-surface temperatures and sea-ice mask
in the model are prescribed from observations. The model is forced by re-analyses
of the European Centre for Medium-range Weather Forecasts (ECMWF) at the lateral
boundaries.

We compared simulations for January 1993 with boundary-layer profiles
measured at the Swedish research station Svca (Dronning Maud Land, Antarctica) and
with radiosonde measurements made at the Georg von Neumayer (GvN) and South Polar
stations for the same period. This comparison was performed in order to study some
model characteristics before the model is used for mass-balance calculations. The
vertical temperature gradient at Svea during the night is overestimated by RACMO,
but corresponds much more closely to the observations than do the ECMWF
re-analyses. in the re-analyses a decoupling of the lowest model layer from the
higher atmosphere occurs. The differences between the absolute temperatures at the
GvN and SP stations and the absolute temperatures at the model gridpoints
corresponding most closely to these sites are less than 5°C. The humidity profiles
indicate that the model generally underestimates the turbulent transport of
moisture from the surface to higher levels.
Surface climate of the interior of the Lambert Glacier basin, Antarctica, from
automatic weather station data
Authors: Allison Ian
Published: November 2017

Data from six automatic weather stations deployed around the interior of the
Lambert Glacier basin, Antarctica, at surface elevations of 1830-2741 m are used
to compile a surface climatology of this part of interior Antarctica for the
period 1994-96. The stations measure air pressure, near-surface wind speed and air
temperature at several levels, wind direction and firn temperatures. The
topography of the basin, which extends more than 800 km inland, controls the
katabatic wind regime and strongly influences the surface climate of the region.
Windiest sites are on the steep coastal slopes, and within the depression of the
Lambert and Mellor Ice Streams where the flow is topographically channelled.
Surface winds here show greater seasonal variation in speed but less variation in
direction than elsewhere. The annual mean temperatures on the relatively steep
slopes on the eastern side of the basin are 4-5°C warmer than at equivalent
altitude on the western side. During winter, near-synchronous synoptic temperature
and pressure increases occur throughout the basin to at least 1000 km from the
coast. There is a consistent pattern of diurnal wind variation in the summer at
all stations, with maximum wind speed at about 0900 LST (local solar time), and
the most easterly direction at 1300 LST.
Comparison of warming trends over the last century around Antarctica from
three coupled models
Authors: Connolley William M. , O'Farrell Siobhan P.
Published: November 2017

We compare observed temperature variations in Antarctica with climate-model
runs over the last century. The models used are three coupled global climate
models (GCMs) — the UKMO, the CSIRO and the MPI forced by the
CO2 increases observed over the last century, and an
atmospheric model experiment forced with observed sea-surface temperatures and
sea-ice extents over the last century. Despite some regions of agreement, in
general the GCM runs appear to be incompatible with each other and with the
observations, although the short observational record and high natural variability
make verification difficult. One of the best places for a more detailed study is
the Antarctic Peninsula where the density of stations is higher and station
records are longer than elsewhere in Antarctica. Observations show that this area
has seen larger temperature rises than anywhere else in Antarctica. None of the
three GCMs simulate such large temperature changes in the Peninsula region, in
either climate-change runs radiatively forced by CO2
increases or control runs which assess the level of model variability.
Surface energy balance and meltwater production for a Dry Valley glacier,
Taylor Valley, Antarctica
Authors: Lewis Karen J. , Fountain Andrew G. , Dana Gayle L.
Published: November 2017

The surface energy balance was calculated to estimate sublimation and melt on
the surface and terminus of Canada Glacier, Taylor Valley, Antarctica, during the
1994-95 and 1995-96 austral summers. Our results indicate that sublimation
accounted for roughly 80% of the observed 1994-95 summer ablation and 40% of the
observed 1995-96 summer ablation on the surface of the glacier. Sublimation Oil
the terminus cliffs appears to be less significant than sublimation on the glacier
surface, probably accounting for at most 10-15% of the measured ablation. Based on
these results, both surface and terminus cliff melt were calculated and compared
with gauged flow in the Glaciol streams. We found thai while the terminus cliffs
represent only 2% of the total ablation zone, they account for 10— 40% of the
total meltwater runoff. Given pur current instrumentation, we can estimate
meltwater discharge from the glacier with an accuracy of ±20%.
Multi-decadal climate variability in the Antarctic region and global
change
Authors: Simmonds Ian , Jones David A. , Walland David J.
Published: November 2017

The characteristics of, and the mechanisms causing, multi-decadal variability
are currently receiving much attention. This undertaking is particularly
challenging in the sub-Antarctic region because of the paucity of data, and the
complexity of the governing physical processes.

In this paper we report on aspects of high-southern-latitude variability
which appear in the European Centre for Medium-range Weather Forecasts twice-daily
analyses for the period 1 January 1980 to 31 August 1996 and in the results of
global climate model experiments. We show that the number of cyclone positions in
the 50-70°S latitude band exhibits considerable interannual variability, as well
as changes on longer time-scales. The seasonal distribution of cyclones is linked
with the “semi-annual oscillation". We show that the variability of this
phenomenon in a 1000 year run of the GFDL coupled model shows “red”
characteristics fand on decadal time-scales is similar to that displayed in the
available observationsi. The interaction with the ocean and sea ice is siressed as
an important factor in determining the nature of climate variability in
sub-Antarctic latitudes.
Late Pleistocene-Holocene sedimentary fluxes of organic carbon and biogenic silica in the northwestern Ross Sea, Antarctica
Authors: Frignani M. , Giglio F. , Langone L. , Ravaioli M. , Mangini A.
Published: November 2017

Eight sediment gravity cores, collected from the joides and Drygalski basins, were analysed in order to understand late Pleistocene-Holocene biogenic flux changes in the Ross Sea, driven by paleoenvironmental changes. Core lithologies and magnetic-susceptibility depth profiles were used for core logging and stratigraphic correlation. Nineteen AMS radiocarbon dates of bulk organic matter were used to set chronological constraints and calculate sediment accumulation rates. These rates, which vary from 1.4-38 cm ka−1. were used to obtain the burial fluxes of biogenic components. The highest fluxes occur in the deepest parts of the basins (TOC, 0.05-0.2 g cm−2ka−1; biogenic silica, 1.5-5 g cm−1ka−1), where as topographic highs show the lowest values (TOC, 0.01-0.1 g cm−2ka−1; biogenic silica, 0.1-1.4 g cm−2ka−1). Dramatic changes in both physical properties and fluxes record the establishment of open marine-sedimentation conditions which occurred first in the joides basin and then, with a delay of ca. 6000 years, in the Drygalski basin. Both TOC and biogenic-silica fluxes increase through the Holocene, though slightly differently. The high fluxes of both10Be and biogenic Ba suggest that sediment accumulation at basin sites is strongly influenced by lateral transport.
Continued northward expansion of the Ross Ice Shelf, Antarctica
Authors: Keys Harry J. R. , Jacobs Stanley S. , Brigham Lawson W.
Published: November 2017

The last major calving event along the Ross Ice Shelf (RIS, Antarctica) front occurred a decade ago, following a substantial increase in the rate of ice-front advance in the few years preceding the event. This “B-9” event, on the eastern part of the front between Edward VII Peninsula and Roosevelt Island, removed ≈ 5100 km2of ice, about 100 years of advance in that sector, but reduced the ice-shelf area by only 1%. Since 1987 the entire ice front has continued to advance, more than regaining the area lost during the B-9 event. The western front is now well north of any position recorded during the last 150 years, and it lias not experienced major calving forat least 90 years. Ice-front heights generally decrease from east to west, but local variability is high. Elevations are relatively low from 171° to 177° W, the location of “warm” Modified Circumpolar Deep Water circulation beneath the outer ice shelf. Modern heights considerably exceed historical heights between 179° Wand 178° E and are lower west of 174° E, probably due to recent dynamic changes such as rifting and the western advance. The general advance of the RIS front and the period of several decades to more than a century that elapses between major calving events is consistent with a relatively stable ice front. This contrasts with several smaller ice shelves along the Antarctic Peninsula and McMurdo Ice Shelf in the Ross Sea which have retreated substantially during the past few decades.
The Arctic ocean-ice system studied by contamination
modelling
Authors: Nazarenko Larissa , Sou Tessa , Eby Michael , Holloway Greg
Published: November 2017

The Arctic represents a relatively pristine frontier that is vulnerable to
pollution. Substances originating at mid latitudes are transported to the
Arctic by atmospheric processes, ocean currents and rivers. These pollutants
can accumulate in the Arctic environment. Testing of nuclear weapons,
dumping of waste and operation of ships, and nuclear power plants also pose
threats.

To investigate possible pollutant pathways we used a multi-level
primitive-equation ocean model, coupled to a dynamic-thermodynamic sea-ice
model. Coupling included conservative transfer of momentum, heat and fresh
water. Atmospheric forcing (wind stress, temperature, humidity, radiation
and heat fresh-water fluxes) was supplied by datasets or bulk formulae. Open
lateral-boundary conditions for the ocean model were supplied either by
datasets (temperature and salinity) or from a larger-scale ocean model
(momentum). Two integrations were compared — one used a centred-difference
advection scheme and viscous damping, while the other used a better
representation of an advection scheme and a sub-gridscale eddy
parameterization.

Tracer simulations showed (1) the importance of good representation of
numerical advection, and (2) the role of eddy interacting with sea-floor
topography (the neptune effect).
Development and evaluation of surface shortwave flux
parameterizations for use in sea-ice models
Authors: Key Jeffrey R. , Liu Yong , Stone Robert S.
Published: November 2017

The surface radiation budget of the polar regions strongly influences ice
growth and melt. Thermodynamic sea-ice models therefore require accurate yet
computationally efficient methods of computing radiative fluxes. In this
paper a new parameterization of the downwelling shortwave radiation flux at
the Arctic surface is developed and compared to a variety of existing
schemes. Parameterized llnxes are compared to in situ measurements using
data for one year at Barrow, Alaska. Our results show that the new
parameterization can estimate the downwelling shortwave flux with mean and
root mean square errors of 1 and 5%, respectively, for clear conditions and
5 and 20% for cloudy conditions. The new parameterization offers a unified
approach to estimating downwelling shortwave fluxes under clear and cloudy
conditions, and is more accurate than existing schemes.
Snow-cover simulations in mountainous regions based on general
circulation model outputs
Authors: Martin Eric , Brun Eric , Durand Yves
Published: November 2017

A meteorological-analysis procedure allowing simulation of the snow cover in
mountainous regions, where the general circulation model orography differs
from the real orography, is described. This procedure uses model outputs to
estimate the data needed to force a snow model. Temperature and
precipitation deduced from three five-year runs were compared to the snow
climatology of the French Alps. The snow cover simulations are very
sensitive to temperature at middle elevations. At high elevations, the
altitude of the equilibrium line is simulated well.
Sensitivity tests of the Canadian Land Surface Scheme (CLASS)
for Arctic tundra
Authors: Tilley Jeffrey S. , Chapman William L. , Wu Wanli
Published: November 2017

We have conducted tests of the Canadian Land Surface Scheme (CLASS V2.5) for
Arctic tundra applications. Our tests emphasize sensitivities to initial
conditions, external forcings and internal parameters, and focus on the
Alaskan North Slope during the summer of 1992. Observational data from the
National Science foundation (NSF), Arctic Systems Science (ARCSS),
Land/Atmosphere/Ice Interactions (LAII) Flux Study is available to serve as
forcing and validation for our simulations.

Comparisons of the runs show strong sensitivities to the composition and
depth of the soil layers, and we find that a minimum total soil depth of 5.0
m is needed to maintain permafrost. The response of the soil to diurnal
variations in forcing is strong, while sensitivities to other internal
parameters, as well as to precipitation, were relatively small. Some
sensitivity to air temperatures and radiative fluxes, particularly the
incoming shortwave flux, was also present. Significant sensitivity to the
specification of the initial water and ice contents of the soil was found,
while the sensitivity to initial soil temperature was somewhat less.
The changing albedo of the Greenland ice sheet: implications for
climate modeling
Authors: Nolin Anne W. , Stroeve Julienne
Published: November 2017

Although the snow albedo feedback mechanism has been shown to amplify global
warming effects in nearly all models of global climate, it continues to be
represented as a simplistic parameterization. Here, we demonstrate how
changes in snow-pack energy-balance drive the seasonal fluctuations in snow
albedo for the Greenland ice sheet. For a detailed, point-based
investigation of the relationship between snowpack energy balance and
albedo, two models are coupled together; one that calculates snow grain-size
and the other that uses those grain-size data as input to a
radiative-transfer code to obtain spectral albedo. These data indicate that
in the near-infrared wavelengths, albedo values drop nearly 20%, during a 10
day period during which grain-sizes increased dramatically. Satellite data
were used to map monthly changes in albedo over the entire Greenland ice
sheet during the spring and summer months. These monthly albedo images
indicate albedo reductions of as much as 80% in coastal regions. Even in
areas that experience little or no melt, albedo decreases of 10–20% were
common. From these results, it is clear that snow albedo parameterizations
for climate models must incorporate the dynamics of snowpack energy
balance.
The climate of antarctica in the UGAMP GCM: Sensitivity to
topography
Authors: Marsiat I. , Bamber J. L.
Published: November 2017

Most spectral general circulation models (GCMs) use an envelope topography
to set on land surface elevations. The UK Universities Global Atmospheric
Modelling Programme General Circulation Model (UGAMP GCM) uses such a
formulation for Antarctica, based on the US Navy 10 are minute charts of the
region. In the marginal regions of the continent, an envelope topography
consistently overestimates the elevation leading to lower-than-observed
surface temperatures. Furthermore, errors in excess of 1000 m exist in the
US Navy data, and the UGAMP GCM treats the major ice shelves as sea ice,
introducing a 12% reduction in the snow-covered area of the continent. Here,
we use a new high-resolution, high-accuracy digital elevation model to
improve the representation of Antarctica in the UGAMP GCM. The effect of
changing the land–sea mask and the topography on the surface temperature,
precipitation and wind held is investigated for both summer and winter runs.
Changing the land–sea mask had a dramatic effect on temperature, producing a
reduction of 13.3°C for the sector west of the Ross Ice Shelf. Using the new
mean topography also introduces substantial differences in temperature, wind
speed and precipitation for summer and winter.
On the role of sea-ice transport in modifying Arctic responses
to global climate change
Authors: Maslanik James , Dunn Jeremy
Published: November 2017

The role of dynamics in modifying the response of the Arctic ice pack to
inter-annually varying forcings and to climate perturbations is investigated
using simulations from a two-dimensional ice model and a global climate
model (GCM). Inter-annual variability in ice-covered area for 1985-93 is
dominated by ice transport, and different transport regimes affect
substantially the response of the ice pack to climate perturbations. The
thermodynamic-only simulations are more sensitive to initial ice conditions,
and respond less than the dynamk-thermodynamic model to small perturbations,
but with a greater response to larger perturbations. Comparisons of GCM
simulations that use different ice treatments highlights the importance of
considering the distribution of ice thickness and extent in assessing
climate-change responses.
Simulation of sea ice in the NCAR Climate System
Model
Authors: Weatherly John W. , Bettge Thomas W. , Briegleb Bruce P.
Published: November 2017

The Climate System Model (CSM) developed at the National Center for
Atmospheric Research (NCAR) consists of atmosphere, land and ocean models,
as well as a dynamic-thermodynamic sea-ice model. The results of sea-ice
simulation using the first coupled climate simulation with the CSM is
presented. It was found that the simulated total-ice areas in both
hemispheres compared well with observations for winter, but were too large
for summer. The numerical solution of the cavitating fluid dynamics was
found to allow excessive ridging of ice, and an ad hoc correction was
implemented. The ice velocities were realistic for the Antarctic, but for
the Arctic were turned toward Alaska and Siberia by modeled winds and
currents. This ice-drift pattern was reflected by ice thickness, which lacks
the observed ridging near Greenland. The results illustrate the sensitivity
of sea ice to the simulation of polar climate and the challenge of modeling
the entire climate system.
Ocean-sea-ice coupling in a global ocean general circulation
model
Authors: Legutke S. , Maier-Reimkr E. , Stössel A. , Hellbach A.
Published: November 2017

A global ocean general circulation model has been coupled with a dynamic
thermodynamic sea-ice model. This model has been spun-up in a 1000 year
integration using daily atmosphere model data. Main water masses and
currents are reproduced as well as the seasonal characteristics of the ice
cover of the Northern and Southern Hemispheres. Model results for the
Southern Ocean, however, show the ice cover as too thin, and there are large
permanent polynyas in the Weddell and Ross Seas. These polynyas are due to a
large upward oceanic heat flux caused by haline rejection during the
freezing of sea ice. Sensitivity studies were performed to test several ways
of treating the sea-surface salinity and the rejected brine. The impact on
the ice cover, water-mass characteristics, and ocean circulation are
described.
Impact of transient increases in atmospheric CO2 on
the accumulation and mass balance of the Antarctic ice sheet
Authors: O’Farrell Siobhan P. , McGregor John L. , Rotstayn Leon D. , Budd William F. , Zweck Christopher , Roland Warner
Published: November 2017

The response of the Antarctic ice sheet to climate change over the next 500
years is calculated using the output of a transient-coupled ocean-atmosphere
simulation assuming the atmospheric CO2 value increases up to
three times present levels. The main effects on the ice sheet on this
time-scale include increasing rates of accumulation, minimal surface
melting, and basal melting of ice shelves. A semi-Lagrangian transport
scheme for moisture was used to improve the model’s ability to represent
realistic rates of accumulation under present-day conditions, and thereby
increase confidence in the anomalies calculated under a warmer climate. The
response of the Antarctic ice sheet to the warming is increased accumulation
inland, offset by loss from basal melting from the floating ice, and
increased ice flow near the grounding line. The preliminary results of this
study show that the change to the ice-sheet balance for the
transient-coupled model forcing amounted to a minimal sea-level contribution
in the next century, but a net positive sea-level rise of 0.21 m by 500
years. This new result supercedes earlier results that showed the Antarctic
ice sheet made a net negative contribution to sea-level rise over the next
century. However, the amplitude of the sea-level rise is still dominated In
the much larger contributions expected from thermal expansion of the ocean
of 0.25 m for 100 years and 1.00 m for 500 years.
Ice-sheet mass balance during the last glacial
maximum
Authors: Ramstein Gilles , Fabre Adeline , Pinot Sophie , Ritz Catherine , Joussaume Sylvie
Published: November 2017

In the framework of the Paleoclimate Modelling Intercomparison Project
(PMIP), simulations of the Last Glacial Maximum (LGM) have- been performed.
More than 10 different atmospheric general circulation models (AGCMs) have
been used with the same boundary conditions: sea-surface temperatures
prescribed by CLIMAP (1981), ice-sheet
reconstruction provided by Peltier
(1994), change in insolation, and reduced CO2 content.
One of the major questions is to investigate whether the simulations of the
LGM are in equilibrium with the prescribed ice-sheet reconstruction.
To answer this question, we have used two different
approaches. First, we analyze the results of a sel of LGM simulations
performed with different versions of the Laboratoire de Meteorolo-gie
Dynamique (LMD) AGCM and study the hydrologic and snow- budgets over the
Laurcntide and Fennoscandian ice sheets. Second, we use the AGCM outputs to
force an ice-sheet model in order to investigate its ability to maintain the
ice sheets as reconstructed by CLIMAP
(1981) or Peltier
(1994).
Areal distribution of the oxygen-isotope ratio in Antarctica: an
assessment based on multivariate models
Authors: Giovinetto Mario B. , Zwally H. Jay
Published: November 2017

Mean oxygen-isotope ratio values relative to standard mean ocean water
(δ18 O, in ‰) reported for 406 sites in Antarctica are
compiled together with data on mean annual surface temperature, latitude,
surface elevation, and mean annual shortest distance to open ocean denoted
by the 20% sea-ice concentration boundary. Stepwise regression analyses with
δ18O as the dependent variable are used as a model-building
procedure based on statistical, rather than physical, criteria. Multivariate
models sensitive to covariation between independent variables are defined
using the whole dataset (N406 where N
denotes the number of sites), as well as sub-sets for areas of conterminous
grounded ice (N206) and ice shell (N110).
The models show improvement over bivariate regression models. Distance to
the open ocean enters all models at the second step. Inversions of the set
and sub-set models applied to a database for 1351 gridpoint locations 100 km
apart (it excludes the regions of Graham Land and eastern Palmer Land) are
used to produce contoured distributions of δ18O. These may be
used to assess the effects of atmospheric advection, as well as derive
ice-flow adjustments for δ18O series obtained from deep-core or
ablation-zone samples. Suggestions are made to improve model
reliability.
Local and global stand-alone tests of the Météo-France snow
parameterization
Authors: Douville Hervé
Published: November 2017

Both observational studies and numerical experiments demonstrate the
sensitivity of the atmosphere to variations in the extent and mass of snow
cover. There is therefore a need for simple but realistic snow
parameterizations in forecast and climate models. A new snow hydrology has
recently been developed at Météo-France. This parameterization has been
validated off-line against field measurements, as well as in a fully
interactive numerical climate experiment. In this study, further tests were
performed in stand-alone mode. The results indicate that the scheme is able
to reproduce snow-cover evolution, both on local and global scales, and some
directions to improve the parameterization further are suggested.
Response of sea-ice models to perturbations in surface heat
flux
Authors: Arbetter T. E. , Curry J. A. , Holland M. M. , Maslanik J. A.
Published: November 2017

There are currently a variety of one- and two-dimensional sea-ice models
being used for climate simulations and sensitivity studies. Though all the
models can be timed to simulate current-day conditions to some degree of
accuracy, the responses of each model to perturbations in forcing from the
atmosphere or ocean are different. Thus, climate-change prediction depends
on the choice of sea-ice model. In this study, the sensitivities of various
sea-ice models to external heat-flux perturbations are examined in a
systematic manner. Starting from similar baseline annual thicknesses, each
model is subjected to an applied heat-flux perturbation to assess icemelt.
Separate experiments are conducted to compare the response of each model to
heat fluxes applied at the atmospheric and the oceanic interfaces. It is
found that the magnitude of the heat-flux perturbation required to melt ice
varies greatly among different models, with the largest difference arising
between models that include ice dynamics vs those that do not. Most models
show an asymmetry in the response to heat-flux perturbations applied at the
top and bottom surfaces of the ice. This study has implications for the
choice of sea-ice models used for climate-change simulations. It also gives
insight to the accuracy required for observations and model simulations of
the surface heat fluxes.
Impact of ocean circulation on regional polar climate
simulations using the Arctic Region Climate System Model
Authors: Bailey David A. , Lynch Amanda H. , Hedström Katherine S.
Published: November 2017

Global climate models have pointed to the polar regions as very sensitive
areas in response to climate change. However, these models often do not
contain representations of processes peculiar to the polar regions such as
dynamic sea ice, permafrost, and Arctic stratus clouds. Further, global
models do not have the resolution necessary to model accurately many of the
important processes and feedbacks. Thus, there is a need for regional
climate models of higher resolution. Our such model (ARCSy M) has been
developed by A. Lynch and W. Chapman. This model incorporates the NCAR
Regional Climate Model (RegCM2) with the addition of Flato–Hibler cavitating
fluid sea-ice dynamics and Parkinson–Washington ice thermodynamic
formulation. Recently work has been conducted to couple a mixed-layer ocean
to the atmosphere–ice model, and a three-dimensional (3-D) dynamical ocean
model, in this case the S-Coordinate Primitive Equation Model (SPEM), to the
ice model. Simulations including oceanic circulation will allow
investigations of the feedbacks involved in fresh-water runoff from sea-ice
melt and sea-ice transport. Further, it is shown that the definition of the
mixed-layer depth has significant impact on ice thermodynamics.
The response of areal snow cover to climate change in a
snowmelt–runoff model
Authors: Rango A.
Published: November 2017

The cryosphere is represented in some hydrological models by the areal
extent of snow cover, a variable that has been operationally available in
recent years through remote sensing. In particular, the snowmelt–runoff
model (SRM) requires the remotely sensed snow-cover extent as a major input
variable. The SRM is well-suited for simulating the hydrological response of
a basin to hypothetical climate change because it is a non-calibrated model.
In order to run the SRM in a climate-change mode, the response of the areal
snow cover to a change in climate is critical, and must be calculated as a
function of elevation, precipitation, temperature, and snow-water
equivalent. For the snowmelt-runoff season, the effect of climate change on
conditions in the winter months has a major influence. In a warmer climate,
winter may experience more rain vs snow events, and more periods of winter
snowmelt that reduce the snow water equivalent present in the basin at the
beginning of spring snowmelt. As a result, the spring snowmelt runoff under
conditions of climate warming will be affected not only by different
temperatures and precipitation, but also by a different snow cover with a
changed depletion rate. A new radiation-based version of the SRM is under
development that will also take changes in cloudiness and humidity into
account, making climate-change studies of the cryosphere even more
physically based.
Year-round pack ice in the Weddell Sea, Antarctica: response and
sensitivity to atmospheric and oceanic forcing
Authors: Geiger Cathleen A. , Ackley Stephen F. , Hibler William D.
Published: November 2017

Using a dynamic-thermodynamic numerical sea-ice model, external oceanic and
atmospheric forcings on sea ice in the Weddell Sea are examined to identify
physical processes associated with the seasonal cycle of pack ice, and to
identify further the parameters that coupled models need to consider in
predicting the response of the pack ice to climate and ocean-circulation
changes. In agreement with earlier studies, the primary influence on the
winter ice-edge maximum extent is air temperature. Ocean heat flux has more
impact on the minimum ice-edge extent and in reducing pack-ice thickness,
especially in the eastern Weddell Sea. Low relative humidity enhances ice
growth in thin ice and open-water regions, producing a more realistic ice
edge along the coastal areas of the western Weddell Sea where dry
continental air has an impact. The modeled extent of the Weddell summer pack
is equally sensitive to ocean heat flux and atmospheric relative humidity
variations with the more dynamic responses being from the atmosphere. Since
the atmospheric regime in the eastern Weddell is dominated by marine
intrusions from lower latitudes, with high humidity already, it is unlikely
that either the moisture transport could be further raised or that it could
be significantly lowered because of its distance from the continent (the
lower humidity source). Ocean heat-transport variability is shown to lead to
overall ice thinning in the model response and is a known feature of the
actual system, as evidenced by the occurrence of the Weddell Polynya in the
mid 1970s.
The effects of snowfall on a snow-ice-thickness
distribution
Authors: Schramm J. L. , Holland M. M. , Curry J. A.
Published: November 2017

Snow falling uniformly on a distribution of ice thicknesses results in a
distribution of snow-cover thicknesses. These snow depths depend on the
amount of snow-fall, the time of year at which it falls, and the thickness
of the underlying ice. The effect of snowfall on snow-ice-thickness
distribution is examined using a single-column ice ocean model. The time at
which snow begins to accumulate, and melt ponds and leads freeze, affects
the surface albedo. The rate of snowfall affects ice-growth rates and, as a
result, the ice-thickness distribution. During the period of rapid ice
growth between the autumn freeze and mid-winter, snow falling on newly
formed ice is rapidly depleted due to sublimation. Snow falling on thicker
ice remains throughout the winter to create a source of melt-water for ponds
and runoff into the ocean.
Modelling the snow cover in a complex Alpine
topography
Authors: Fierz Charles , Plüss Christian , Martin Eric
Published: November 2017

The areal distribution of snow cover and the variability of its
characteristics were investigated at various locations in the eastern Swiss
Alps. An areal energy-balance (AEB) model was used to calculate the
predominant energy fluxes at the snow–atmosphere interface based on
automatic meteorological measurements as input. By coupling the AEB model
with a one-dimensional, physically based mass and energy-balance model of
the snowpack, temperature distribution as well as energy and mass flow in
the snowpack were simulated at three different locations in the
topographically complex environment at Weissfluhjoch-Davos, 2540 m a.s.l. On
a horizontal test site, calculated energy fluxes and characteristics of the
snow cover are in good agreement with their measured counterparts. On
inclined slopes, the temperature distribution is well represented by the
coupled models, but the snow depth and density are not yet satisfactorily
simulated. This discrepancy may be attributed to inhomogeneous accumulation
and deposition of snow on the weather and lee sides.
A three-dimensional climate—ice-sheet model applied to the Last
Glacial Maximum
Authors: Huybrechts Philippe , T’siobbel Stephen
Published: November 2017

A quasi-three-dimensional (3-D) climate model (Sellers, 1983) was used to simulate the climate of the
Last Glacial Maximum (LGM) in order to provide climatic input for the
modelling of the Northern Hemisphere ice sheets. The climate model is
basically a coarse-gridded general circulation (GCM) with simplified
dynamics, and was subject to appropriate boundary conditions for ice-sheet
elevation, atmospheric CO2 concentration and orbital parameters.
When compared with the present-daysimulation, the simulated climate at the
Last Glacial Maximum is characterized by a global annual cooling of 3.5°C
and a reduction in global annualprecipitation of 7.5%, which agrees well
with results from other, more complex GCMs. Also the patterns of temperature
change compare fairly with mostother GCM results, except for a smaller
cooling over the North Atlantic and the larger cooling predicted for the
summer rather than for the winter over Eurasia.

The climate model is able to simulate changes in Northern Hemisphere
tropospheric circulation, yielding enhanced westerlies in the vicinity of
the Laurentide and Eurasian ice sheets. However, the simulated precipitation
patterns are less convincing, and show a distinct mean precipitation
increase over the Laurentide ice sheet. Nevertheless, when using the
mean-monthly fields of LGM minus present-day anomalies of temperature and
precipitation rate to drive a three-dimensional thermomechanical ice-sheet
model, it was demonstrated that within realistic bounds of the ice-flow and
mass-balance parameters, veryreasonable reconstructions of the Last Glacial
Maximum ice sheets could be obtained.
Historical variability in Northern Hemisphere spring
snow-covered area
Authors: Brown Ross D.
Published: November 2017

Observed and reconstructed snow-cover duration data from stations covering
southern Canada, the Great Plains, the former Soviet Union and China were
used to reconstruct spring snow-covered area over North America (NA) and
Eurasia from 1915 to 1985. A combination of nine regions from NA and five
from Eurasia were able to explain 81% and 67%, respectively, of the variance
in satellite-derived sprint; snow-covered area (SCA) for each continent. The
results suggested sprint; SCA had decreased significantly in Eurasia this
century, but there was no evidence of a similar long-term decrease in NA
spring SCA. Considerable caution should be used when interpreting these
results because of the short period of calibration, and because of the
less-than-optimal distribution of station data. Nonetheless, the
reconstructed results are consistent with observed spring-temperature
trends, which show a significant increase over Eurasia, but none Over
NA.
Relationship between snow cover and atmospheric circulation,
central North America, winter 1988
Authors: Derksen Chris , Misurak Kkevin , Ledrew Ellsworth , Piwowar Joe , Goodison Barry
Published: November 2017

The stochastic relationships between terrestrial snow water equivalent (SWE)
and measures of the atmospheric circulation were investigated for the
Canadian Prairies and the American Great Plains for the winter of 1988.
Snow-cover extent, derived from EASE-grid SSM/I satellite data, and griddcd
atmospheric data from the National Meteorological Center were averaged at
five day intervals. Principal components analysis (PCA) were performed for
the time series of SSM/I snow-cover imagery as well as for 700 mb
geopotential height and temperature, 500 mb height and 700–500 mb thickness.
Canonical correlation analysis of the derived principal component weights
was used to identify relationships between atmospheric variables and SWE.
Results of the PCA indicate that a high degree of variance in upper air
variables (>75%) can be explained by the first three principal
components, while the first three SWE components account for over 90% of the
variance in the original data. Results of the canonical correlation analysis
show positive relationships between snow-cover accumulation and a meridional
pressure distribution pattern, while snow ablation is linked to a zonal
atmospheric pressure pattern.
The perennial ice cover of the Beaufort Sea from active- and
passive-microwave observations
Authors: Kwok R. , Comiso J.C.
Published: November 2017

The perennial ice concentration in the Beaufort Sea was examined using
active- and passive-microwave observations. We compared the ice type and
concentration estimates from SSM/I and ERS-1 SAR data over a seasonal cycle
from January 1992 to January 1993. It was found the multi-year (MY)
ice-concentration estimates from the SAR data were very stable and were
nearly equivalent to the ice concentration estimated at the end of the
previous summer. We contrast this with the variability of the MY
ice-concentration and ice-fraction estimates obtained using the NASA Team
algorithm. The passive- and active-microwave algorithms provide total ice
concentrations that are comparable during the winter, hut the passive
estimates are significantly lower during the summer. Passive-microwave
estimates of multi-year-ice concentrations are consistently lower (up to
30%) than those from the SAR data. We discuss reasons for these
discrepancies and the possible biases introduced by the active and passive
algorithms.
Surface turbulent fluxes over pack ice inferred from TOVS
observations
Authors: Lindsay R.W. , Francis J. A. , Persson P. O. G. , Roterock D. A. , Schweiger A.J.
Published: November 2017

A one-dimensional, atmospheric boundary-layer model is coupled to a
thermodynamic ice model to estimate the surface turbulent fluxes over thick
sea ice. The principal forcing parameters in this time-dependent model are
the air temperature, humidity, and wind speed at a specified level (either
at 2 m or at 850 mb) and the down-welling surface radiative fluxes, The free
parameters are the air temperature, humidity, and wind-speed profiles below
the specified level, the surface skin temperature and ice-temperature
profile, and the surface turbulent fluxes. The goal is to determine how well
we can estimate the turbulent surface heat and momentum fluxes using forcing
parameters from atmospheric temperatures and radiative fluxes retrieved Irom
the TlROS-N Operational Vertical Sounder TOVS) data.

Meteorological observations from the Lead Experiment (LeadEx, April 1992)
ice camp are used to validate turbulent fluxes computed with the surface
observations, and the results are used to compare with estimates based on
radiosonde observations or with estimates based on TOVS data. We and that
the TOVS-based estimates of the stress are significantly more accurate than
those found with a constant geostrophic drag coefficient, with a rool mean
square error about half as large. This improvement is due to stratification
effects included in the boundary-layer model. The errors in the sensible
heat flux estimates, however, are large compared Io the small mean values
observed during the field experiment.