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A Review of Antarctic Surface Snow Isotopic Composition : Observations, Atmospheric Circulation, and Isotopic Modeling

TL;DR: In this article, a database of surface Antarctic snow isotopic composition is constructed using available measurements, with an estimate of data quality and local variability, and the capacity of theoretical isotopic, regional, and general circulation atmospheric models to reproduce the observed features and assess the role of moisture advection in spatial deuterium excess fluctuations.
Abstract: A database of surface Antarctic snow isotopic composition is constructed using available measurements, with an estimate of data quality and local variability. Although more than 1000 locations are documented, the spatial coverage remains uneven with a majority of sites located in specific areas of East Antarctica. The database is used to analyze the spatial variations in snow isotopic composition with respect to geographical characteristics (elevation, distance to the coast) and climatic features (temperature, accumulation) and with a focus on deuterium excess. The capacity of theoretical isotopic, regional, and general circulation atmospheric models (including “isotopic” models) to reproduce the observed features and assess the role of moisture advection in spatial deuterium excess fluctuations is analyzed.

Summary (2 min read)

1. Introduction

  • Regional Antarctic temperature reconstructions are also essential for the comparison between observed past climatic changes and simulations performed by AGCMs, conducted only for the inland East Antarctic plateau (Masson-Delmotte et al. 2006).
  • To analyze the stable isotopic composition of snowfall in a model framework that is compatible with the observed climatology, several methods must be combined.

2. A database of Antarctic snow isotopic composition

  • A. Sampling sites and related documentation Table 2 presents the list and references of the various sources of information compiled to produce the full Antarctic database (available as an Excel file online at http://www.lsce.ipsl.fr/Pisp/24/valerie.masson-delmotte. html).
  • Annual mean surface air or firn temperatures are available for only 811 sites; the situation is even more restricted for annual mean accumulation data, available only for 322 sites (Fig. 2).
  • The first two criteria are expected to reflect the quality of the isotopic measurements and sample preservation; the last three criteria have been defined with respect to the temporal scale and resolution of the samples, with the purpose of building “climatologies” of surface snow isotopic composition.
  • The authors now describe the range of variability of D, 18O, and deuterium excess data, both spatially (from site to site) and temporally (within one site when several measurements have been averaged to produce the local average value).
  • The amplitude of local D range (difference between maximum and minimum values of individual sample measurements at one location) varies between 4.9‰ and 262.3‰, with a mean range of 74.1‰.

D and 88% of the 18O spatial variance:

  • The observations show isotopic values that are less depleted than the calculation (positive anomalies) on the flanks of the ice sheet (at elevations from 1000 to 2000 m) and inland West Antarctica, whereas they show isotopic values that are more depleted than the calculation (negative anomalies) in the central Antarctic Peninsula and the central East Antarctic plateau.
  • To assess the spatial variations of this slope, the authors have developed a methodology to estimate local slopes.
  • The distribution of deuterium excess as a function of D (Fig. 6d) now relies on 789 data points, including new traverse data available from the coast to the interior of East Antarctica and 269 data points from the Taylor Valley in the Dry Valleys (with many negative deuterium excess values).

In the Lambert Glacier area, deuterium excess values

  • Atmospheric models can be used to analyze the vertical moisture advection to Antarctica (see section 3) and test this hypothesis.
  • The observed deuterium excess spatial distribution also reflects changes in the D– 18O slope depending on the range of isotopic values (Fig. 4).
  • These slope uncertainties have been obtained from a Monte Carlo method using 1000 random subsets.

7.30‰ (‰) 1 are observed in central East Antarctic ice cores (Vimeux et al. 1999; Stenni et al. 2001).

  • Different moisture origins at coastal versus inland locations should influence the distribution of deuterium excess, but also 18O, D, and their relationships to local climatic parameters.
  • Changes in isotope– temperature slopes between locations may be related to atmospheric transport paths.
  • In fact, such spatial slopes very likely include the combined effects of distillation, including temperature gradients between source and site temperatures, and equilibrium fractionation effects along different ranges of temperatures.
  • Isotopic models are used in the next section to assess the relative weight and role of these different physical processes on the Antarctic snow isotopic composition.

3. Model–data comparisons

  • The authors also analyze the capability of AGCMs to simulate this observed distribution.
  • The isotopic AGCMs offer the advantage of consistent simulations of climate and isotopic processes, but make it difficult to isolate the impact of each process on the isotopic composition of precipitation (Table 1).
  • Diagnostic of the fraction of simulated fifth-generation Pennsylvania State University (PSU)–National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5) annual precipitation that is removed from the surface by sublimation (Bromwich et al. 2004). rence) condensation temperature, estimated by the temperature at the vertical level of the maximum condensed moisture (Helsen et al. 2007).
  • The model–data comparison therefore points to the following two systematic model biases: (i) a lack of isotopic depletion, even in AGCMs simulating a correct range of Antarctic surface temperature, and (ii) an underestimation of moisture supply to inland Antarctica (specifically at temperatures below 30°C).

4. Conclusions and perspectives

  • The authors compilation of surface Antarctic snow composition provides better spatial coverage than earlier studies, although it is still strongly biased toward East Antarctic locations.
  • Systematic measurements of water vapor and snow isotopic composition should allow us to disentangle the effect of depositional and postdepositional processes.
  • Intensive efforts based on accumulation histories derived from ice cores suggest that, despite a warming detected in winter tropospheric temperature in Antarctica during the past decades (Turner et al. 2006), there is no significant change in Antarctic accumulation since the International Geophysical Year in 1957–58 (Monaghan et al. 2006).
  • This database confirms earlier findings regarding the spatial variability of the isotope distribution in relation to geographical parameters (latitude, distance from the coast, and elevation).
  • It shows regional signatures, with variations mostly within 20%–.

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A Review of Antarctic Surface Snow Isotopic Composition: Observations, Atmospheric
Circulation, and Isotopic Modeling*
V. MASSON-DELMOTTE,
a
S. HOU,
b
A. EKAYKIN,
c
J. JOUZEL,
a
A. ARISTARAIN,
d
R. T. BERNARDO,
e
D. BROMWICH,
f
O. CATTANI,
a
M. DELMOTTE,
a
S. FALOURD,
a
M. FREZZOTTI,
g
H. GALLÉE,
h
L. GENONI,
i
E. ISAKSSON,
j
A. LANDAIS,
a,k
M. M. HELSEN,
l
G. HOFFMANN,
a
J. LOPEZ,
m
V. MORGAN,
n
H. MOTOYAMA,
o
D. NOONE,
p
H. OERTER,
q
J. R. PETIT,
h
A. ROYER,
a
R. UEMURA,
o
G. A. SCHMIDT,
r
E. SCHLOSSER,
s
J. C. SIMÕES,
e
E. J. STEIG,
t
B. STENNI,
i
M. STIEVENARD,
a
M. R. VAN DEN BROEKE,
l
R. S. W. VAN DE WAL,
l
W. J. VAN DE BERG,
l
F. VIMEUX,
a,u
J. W. C. WHITE
v
a
Laboratoire des Sciences du Climat et de l’Environnement, IPSL/CEA-CNRS-UVSQ, Saclay, Gif-sur-Yvette, France
b
Laboratory of Cryosphere and Environment, Chinese Academy of Sciences, Lanzhou, China
c
Arctic and Antarctic Research Institute, St. Petersburg, Russia
d
Laboratorio de Estratigrafía Glaciar y Geoquímica del Agua y de la Nieve, Instituto Antártico Argentino, Mendoza, Argentina
e
Nucleo de Pesquisas Antarcticas e Climaticas, Departmento de Geografia, Instituto de Geociencias, Universidade Federal do Rio
Grande do Sul, Porto Alegre, Brazil
f
The Ohio State University, Columbus, Ohio
g
ENEA, Rome, Italy
h
Laboratoire de Glaciologie et de Géophysique de l’Environnement, CNRS-Université Joseph Fourier, Saint Martin d’Hères, France
i
Department of Geological, Environmental and Marine Sciences, University of Trieste, Trieste, Italy
j
Norwegian Polar Institute, Tromsø´, Norway
k
Earth Science Institute, Hebrew University, Jerusalem, Israel
l
Institute for Marine and Atmospheric Research, Utrecht University, Utrecht, Netherlands
m
Departamento de Geologica y Geoquimica, Universidad Autonoma de Madrid, Madrid, Spain
n
Antarctic Climate and Ecosystems CRC, and Australian Antarctic Division, Hobart, Australia
o
National Institute of Polar Research, Research Organization of Information and Systems, Tokyo, Japan
p
Department of Atmospheric and Oceanic Sciences, and Cooperative Institute for Research in Environmental Sciences, University of
Colorado, Boulder, Colorado
q
Alfred-Wegener-Institute für Polar und Meeresforschung, Bremerhaven, Germany
r
NASA GISS, New York, New York
s
Institute of Meteorology and Geophysics, University of Innsbruck, Innsbruck, Austria
t
Department of Earth and Space Sciences, University of Washington, Seattle, Washington
u
UR Greatice, IRD, Paris, France
v
INSTAAR, Boulder, Colorado
(Manuscript received 6 July 2007, in final form 27 November 2007)
ABSTRACT
A database of surface Antarctic snow isotopic composition is constructed using available measurements,
with an estimate of data quality and local variability. Although more than 1000 locations are documented,
the spatial coverage remains uneven with a majority of sites located in specific areas of East Antarctica. The
database is used to analyze the spatial variations in snow isotopic composition with respect to geographical
characteristics (elevation, distance to the coast) and climatic features (temperature, accumulation) and with
a focus on deuterium excess. The capacity of theoretical isotopic, regional, and general circulation atmo-
spheric models (including “isotopic” models) to reproduce the observed features and assess the role of
moisture advection in spatial deuterium excess fluctuations is analyzed.
* European Project for Ice Coring in Antarctica Publication Number 188 and Laboratoire des Sciences du Climat et l’Environnement
Contribution Number 2739.
Corresponding author address: Valérie Masson-Delmotte, Laboratoire des Sciences du Climat et de l’Environnement, IPSL/CEA-
CNRS-UVSQ, UMR 1572, Bat 701, L’Orme des Merisiers CEA, Saclay, 91 191 Gif-sur-Yvette CEDEX, France.
E-mail: valerie.masson@cea.fr
1J
ULY 2008 M A S SON-DELMOTTE ET AL. 3359
DOI: 10.1175/2007JCLI2139.1
© 2008 American Meteorological Society
JCLI2139

1. Introduction
Since the 1950s, it has been observed that the stable
isotopic composition of precipitation in the mid- and
high latitudes is related to air temperature (Dansgaard
1953; Epstein and Mayeda 1953; Craig 1961). In Ant-
arctica (Fig. 1), surface snow was sampled along
traverses to inland stations and firn temperature mea-
surements were used as indicators of annual mean sur-
face temperature (Epstein et al. 1963). Early studies
were conducted to determine the spatial relationship
between precipitation isotopic composition and local
temperature (Lorius et al. 1969).
Assuming that this relationship remains valid over
time, these calibrations were then used as an isotopic
thermometer to quantify past changes in temperature
based on the stable isotopic composition of deep ice
cores, such as the recently obtained Eupropean Project
for Ice Coring in Antarctica (EPICA) ice cores drilled
at Dome C (DC; EPICA Community Members 2004)
and in Dronning Maud Land (DML; EPICA Commu-
nity Members 2006). In Greenland, the use of the spa-
tial isotopetemperature slope has been challenged by
alternative paleothermometry methods, such as the in-
version of the borehole temperature profile (Cuffey et
al. 1992; Johnsen et al. 1995), and the thermal and
gravitational diffusion of air in the firn arising during
abrupt climate changes (Severinghaus et al. 1998; Lang
et al. 1999; Landais et al. 2004a,b,c).
In central East Antarctica, inversion of the borehole
temperature profiles is problematic because of the low
accumulation rates (Salamatin et al. 1998). Because
Antarctic climate changes are less rapid than in Green-
land, the gas fractionation method is problematic and
cannot be used easily to quantify past temperature
changes (Caillon et al. 2001; Landais et al. 2006). How-
ever, the stable isotope profiles derived from East Ant-
arctic ice cores can be directly used to estimate past
changes in accumulation through relationships between
stable isotopes, air temperature, and saturation vapor
pressure that are included in inversed glaciological dat-
ing methods (Parrenin et al. 2001). The dating of deep
ice cores itself, when constrained by age markers, can
be used to assess the stability of the isotopetempera-
ture relationship back in time. When applied to inland
Antarctic sites, such as Vostok (Parrenin et al. 2001),
Dome Fuji (Watanabe et al. 2003), or EPICA Dome C
(EPICA Community Members 2004), inverse methods
suggest that the present-day-observed isotopetemper-
ature slopes remain valid for past periods within 20%
30%, consistent with estimates provided by atmo-
spheric general circulation models (AGCMs) (Jouzel et
al. 2003).
Obtaining past temperature reconstructions together
with a precise estimate of their uncertainties remains
critical for the understanding of the natural pacing of
Antarctic temperature (and accumulation) changes. A
recent synthesis effort conducted over the past 200 yr
using well-dated ice cores has revealed strong interan-
nual and decadal variability, with antiphase behavior
between the Antarctic Peninsula and the inland sites,
and the impact of the Southern Hemisphere (SH) an-
FIG. 1. Map of Antarctic topography showing (left) the names of different geographical sectors mentioned in the text and (right)
the main deep ice core sites together with the main ice divide.
3360 JOURNAL OF CLIMATE VOLUME 21

nular mode on Antarctic temperature variability
(Schneider et al. 2006), together with the variability
associated with ENSO (Schneider and Noone 2007).
The Antarctic-scale coherence of temperature change
remains uncertain at lower frequencies. A stack of five
central Antarctic ice cores stable isotope records also
suggests a small magnitude (0.2°C) of common cen-
tennial-scale temperature variability (Goosse et al.
2004). Regional Antarctic temperature and accumula-
tion reconstructions are essential for forcing Antarctic
ice sheet models and for understanding the Antarctic
ice sheet mass balance and dynamical reaction to
changing climate and sea level. Because stable isotope
records may be affected by changes in moisture origin,
syntheses of stable isotope records should be per-
formed over areas with similar moisture origins
(Reijmer et al. 2002). Regional Antarctic temperature
reconstructions are also essential for the comparison
between observed past climatic changes and simula-
tions performed by AGCMs, conducted only for the
inland East Antarctic plateau (Masson-Delmotte et al.
2006).
In parallel, the factors controlling the isotopic com-
position of Antarctic snowfall have been analyzed
based on a hierarchy of modeling approaches (Table 1).
Distillation models calculate the theoretical fraction-
ation that occurs along a cooling path with prescribed
initial evaporation and condensation conditions. Such
models have been used to assess the impact of equilib-
rium and kinetic fractionation processes on the snowfall
isotopic composition (Merlivat and Jouzel 1979; Jouzel
and Merlivat 1984). The second-order isotopic param-
eter deuterium excess d
D 8
18
O (Dansgaard
1964) is expected to be highly sensitive to kinetic effects
occurring either during evaporation at the ocean sur-
face or during atmospheric transport (e.g., reevapora-
tion of droplets or ice crystal formation). The observed
high deuterium excess values of inland Antarctic snow
cannot be simulated without taking into account kinetic
fractionation in supersaturation conditions over ice
crystals (Jouzel and Merlivat 1984; Salamatin et al.
2004). Sensitivity tests conducted with distillation mod-
els suggest that spatial variations of deuterium excess in
Antarctica may reflect, at least partly, different mois-
ture origins (Ciais and Jouzel 1994; Ciais et al. 1995;
Kavanaugh and Cuffey 2003; Masson-Delmotte et al.
2004).
AGCMs equipped with the explicit representation of
water-stable isotopes (Joussaume et al. 1984; Jouzel et
al. 1987b, 1991; Hoffmann et al. 2000) allow us to dis-
entangle the different factors involved in the spatial
(Brown and Simmonds 2004; Schmidt et al. 2005), sea-
sonal (Koster et al. 1992; Delmotte et al. 2000), inter-
annual (Werner et al. 2001; Werner and Heimann 2002;
Noone and Simmonds 2002a), or glacialinterglacial
changes (Delaygue et al. 2000) in Antarctic snow iso-
topic composition. They offer the advantage of a con-
sistent frame where tracers can be used to tag moisture
of different geographical origins (Koster et al. 1986;
Delaygue et al. 2000).
From these modeling efforts, it appears that the key
factors controlling the observed distribution of stable
isotopes in Antarctic snow are related to spatial
changes of the integrated condensation temperature
(including changes along the vapor trajectory, vertical
changes, and the intermittency of snowfall days), and
the origin of moisture (transported either at different
elevations or from different geographical areas). In
principle, condensation temperature during snowfall
episodes should be the relevant climatic parameter
used to analyze the spatial distribution of stable iso-
topes. Because only very few records of Antarctic con-
densation temperature are available, inversion tem-
perature has been used as a surrogate for condensation
temperature (Jouzel and Merlivat 1984). A detailed
study for Vostok (Ekaykin 2003) confirmed the validity
of this assumption for central Antarctica. However, this
study highlighted that most of the local accumulation
does not arise from cloud condensation, but from clear-
sky deposition of diamond dust. Until now, the com-
parison between AGCMs and isotopic data has not
been focused on the different types of precipitation.
Biases of the simulated spatial distribution for the
Antarctic surface air temperature range and of the
amount or origin of snowfall can induce difficulties in
the comparison of AGCM results with Antarctic isoto-
pic data. To analyze the stable isotopic composition of
snowfall in a model framework that is compatible with
the observed climatology, several methods must be
combined. For example, background fields of transport
that are more consistent with observations can be pro-
vided by nudging AGCMs with reanalyses (Yoshimura
et al. 2004; Noone 2006). Regional atmospheric models
can also be used to simulate local features of the Ant-
arctic atmospheric circulation and to analyze the factors
controlling the regional origin of Antarctic moisture.
Atmospheric reanalyses are used to calculate back
trajectories for individual Antarctic snowfall events.
Along the back trajectories, distillation models can be
implemented to estimate the snowfall isotopic compo-
sition (Helsen et al. 2007). Because the backward tra-
jectories generally do not capture the evaporation pro-
cess in the moisture source areas, monthly mean fields
of atmospheric water vapor isotopic composition simu-
lated by general circulation models have been used to
initialize vapor isotopic composition for trajectory cal-
1JULY 2008 M A S SON-DELMOTTE ET AL. 3361

TABLE 1. Hierarchy of modeling approaches used to analyze the processes responsible for the isotopic composition of Antarctic
snowfall.
Method References Advantages Limitations
Rayleigh or mixed phase
distillation model
Jouzel and Merlivat (1984),
Jouzel (1986),
Fisher (1990), Ciais and
Jouzel (1994), Kavanaugh
and Cuffey (2003), and
Salamatin et al. (2004)
Key microphysical processes
represented
Assumption on initial evaporation
conditions (closure equation or
iso-AGCM water vapor fields)
Ability to perform sensitivity tests
on different aspects of the
fractionation along the water
cycle path (evaporation,
supersaturation, etc.)
Assumption on the relationship
between condensation and
surface temperature
Poor representation of convection
processes (not a key limitation
for inland Antarctica)
Atmospheric general
circulation models
equipped with the
explicit modeling of
water-stable isotopes
Joussaume et al. (1984),
Jouzel et al. (1987b),
Hoffmann et al. (1998,
2000), Werner and
Heimann (2002), Noone
and Simmonds (1998), and
Schmidt et al. (2005)
Intrinsic model coherency Potential biases in model
climatologies, especially in
Antarctica
Full coupling between
meteorological conditions and
distillation
Limitations resulting from model
resolution and adaptation of
parameterizations for
Antarctica (katabatic winds,
boundary layer processes,
stratospheric processes, cloud
microphysics)
Possibility to explore the temporal
stability of spatial relationships
in response to various climate
forcings
Difficult to isolate the relative role
of different processes (moisture
origin, trajectory, condensation,
etc.)
Identification of synoptic
weather characteristics
and back trajectories for
snowfall events using
atmospheric reanalyses
Reijmer et al. (2002) and
Schlosser et al. (2004)
Realistic synoptic framework Difficult to isolate the relative role
of different processes (moisture
origin, trajectory, condensation,
etc.) on final precipitation
isotopic composition
Possibility to relate clusters of
snowfall events to synoptic
weather systems using their
isotopic composition
Difficult to follow moisture
transport in the back trajectories
Simple isotopic model
calculations along back
trajectories using
AGCM water vapor
climatological
distribution
Helsen et al. (2007) Quantify the impact of airmass
origins on final moisture
isotopic composition
Possible incoherencies between
iso-AGCM water vapor isotopic
composition fields and back
trajectories from reanalyses
No hypothesis on condensation
temperature (derived from
reanalyses)
Limited representation of
convective processes
Nudging of iso-AGCMs
with reanalyses
Noone (2006) Analysis of model results in a
dynamical framework coherent
with observations
See section on iso-AGCM
regarding AGCM limitations
Regional atmospheric
models nudged with
reanalyses
Gallee et al. (2001),
Bromwich et al. (2004),
and van den Broeke and
van Lipzig (2005)
Good representation of key
processes relevant for Antarctic
precipitation (cloud
microphysics, boundary layer,
postdepositional effects)
Difficult to follow moisture
transport
Difficult to isolate the relative role
of different processes (moisture
origin, trajectory, condensation,
etc.) on final precipitation
isotopic composition
Regional atmospheric
models with the explicit
modeling of stable
isotopes
Sturm et al. (2005) Advantages of mesoscale models
with the coherency between
atmospheric dynamics and
isotopes of water
Not yet achieved for Antarctica
3362 JOURNAL OF CLIMATE VOLUME 21

culations (Helsen et al. 2006). Backward air trajectories
calculated for different Antarctic areas (Reijmer et al.
2002; Helsen et al. 2006) showed different moisture
transport paths for coastal areas, where seasonal con-
vection and cyclonic activity play a large role, and in-
land sites, where clear-sky precipitation may be a dom-
inant contribution to local snowfall (Ekaykin 2003).
Parallel with these improvements on the modeling
side, intensive field campaigns have been carried out in
various sectors of Antarctica, including coordinated in-
ternational traverses and presite surveys in search of
optimal deep-drilling sites (Table 2). In this work, we
have compiled a database of the available measure-
ments of snowfall, surface snow, or firn core isotopic
composition, taking into account their local variability.
This database predominantly includes published mea-
surements of Antarctic snow isotopic composition, and
some unpublished data (Table 2) prior to the new field
campaigns planned during the fourth International Po-
lar Year.
The second section describes the various datasets,
the quality control methodology, and the assessment of
uncertainties, as well as the resulting spatial distribu-
tion of Antarctic snow-stable isotopic composition. The
third section is focused on the comparison between
these observations and a variety of model results based
on simple isotopic models, regional atmospheric mod-
els, and isotopic AGCMs. The main outcomes of the
paper and suggested ways forward are presented in the
conclusions.
2. A database of Antarctic snow isotopic
composition
a. Sampling sites and related documentation
Table 2 presents the list and references of the various
sources of information compiled to produce the full
Antarctic database (available as an Excel file online at
http://www.lsce.ipsl.fr/Pisp/24/valerie.masson-delmotte.
html). When available, we have included geographical
information on the sampling location, such as annual
mean temperature (estimated either from firn tempera-
ture measurements or automatic weather station sur-
face air monitoring), latitude, longitude, and elevation
(Fig. 2). In some cases, estimates of local accumulation
rates are available, based on the identification of an-
nual layers and reference horizons (e.g., Frezzotti et al.
2005). To quantify the continentality of the sites, we
have estimated the horizontal distance to the nearest
coast using the Antarctic coastline (this measurement
may not reflect the distance along moisture trajectories,
which is important for isotope physics). We have not
included error bars on the estimates of annual mean
temperature and accumulation rate because of a lack of
consistent methodologies to evaluate these uncertain-
ties.
The surface snow isotopic composition has been
measured from direct precipitation sampling at a few
sites [Global Network for Isotopes in Precipitation
(GNIP) stations from the following International
Atomic Energy Agency (IAEA) stations: Neumayer,
Dumont dUrville, Vostok, and Dome Fuji] over vary-
ing durations, sometimes over 1 yr (Motoyama et al.
2005; Fujita and Abe 2006) or, for Neumayer, continu-
ously since 1981 (Schlosser et al. 2004). Most surface
snow samples have been collected along traverses con-
ducted by individual groups or coordinated within the
International Trans-Antarctic Scientific Expeditions
(ITASE; Mayewski et al. 2005).
Surface snow-sampling procedures differ signifi-
cantly from one site to another. In some cases, shallow
snow cores or pits, typically 1 m deep, were sampled
and one or several measurements were performed. In
other cases, longer firn or ice cores have been analyzed
with a subannual resolution. The database includes a
description of the depth range and, if available, the
temporal range (dating). In places where deep firn or
ice cores have been drilled, meteorological data and
detailed snow measurements are available. In some
cases, there is no seasonal resolution either because of
the low accumulation rates or the crude measurement
resolution.
Finally, for each location we have reported the snow
isotopic composition (
D,
18
O, and deuterium excess
d), in per mille () with respect to the Vienna Standard
Mean Ocean Water (V-SMOW). When more than five
measurements were performed at the same location
(corresponding either to detailed measurements on a
firn profile or to seasonal samples of snowfall), we have
also included basic statistics (number, mean, maximum,
minimum values, and standard deviation of the mea-
surements) in the table. The country where the mea-
surements were performed is also indicated.
The final database includes 1279 locations, out of
which 938 have
D measurements, 1125 have
18
O
measurements, and 794 have both isotopes, making it
possible to calculate the deuterium excess (Fig. 3). For
each site, deuterium excess values were calculated from
individual measurements of
D and
18
O conducted on
the same samples. Note that for each site we have cal-
culated an average of all
D data available, an average
of all
18
O data available, and an average of deuterium
excess data (which may be on a restricted subset of data
for which both isotopes have been measured). There-
fore, the reported deuterium excess is not systemati-
cally identical to
D 8
18
O calculated from the mean
1JULY 2008 M A S SON-DELMOTTE ET AL. 3363

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Journal ArticleDOI
TL;DR: The Southern Hemisphere climate system varies on timescales from orbital, through millennial to sub-annual, and is closely coupled to other parts of the global climate system as discussed by the authors.
Abstract: The Antarctic climate system varies on timescales from orbital, through millennial to sub-annual, and is closely coupled to other parts of the global climate system. We review these variations from the perspective of the geological and glaciological records and the recent historical period from which we have instrumental data (the last 50 years). We consider their consequences for the biosphere, and show how the latest numerical models project changes into the future, taking into account human actions in the form of the release of greenhouse gases and chlorofluorocarbons into the atmosphere. In doing so, we provide an essential Southern Hemisphere companion to the Arctic Climate Impact Assessment.

559 citations

Journal ArticleDOI
TL;DR: In this article, an overview of the various measurement techniques, related difficulties, and limitations of data interpretation; describe spatial characteristics of East Antarctic SMB and issues related to the spatial and temporal representativity of measurements; and provide recommendations on how to perform in situ measurements.
Abstract: The East Antarctic Ice Sheet is the largest, highest, coldest, driest, and windiest ice sheet on Earth. Understanding of the surface mass balance (SMB) of Antarctica is necessary to determine the present state of the ice sheet, to make predictions of its potential contribution to sea level rise, and to determine its past history for paleoclimatic reconstructions. However, SMB values are poorly known because of logistic constraints in extreme polar environments, and they represent one of the biggest challenges of Antarctic science. Snow accumulation is the most important parameter for the SMB of ice sheets. SMB varies on a number of scales, from small-scale features (sastrugi) to ice-sheet-scale SMB patterns determined mainly by temperature, elevation, distance from the coast, and wind-driven processes. In situ measurements of SMB are performed at single points by stakes, ultrasonic sounders, snow pits, and firn and ice cores and laterally by continuous measurements using ground-penetrating radar. SMB for large regions can only be achieved practically by using remote sensing and/or numerical climate modeling. However, these techniques rely on ground truthing to improve the resolution and accuracy. The separation of spatial and temporal variations of SMB in transient regimes is necessary for accurate interpretation of ice core records. In this review we provide an overview of the various measurement techniques, related difficulties, and limitations of data interpretation; describe spatial characteristics of East Antarctic SMB and issues related to the spatial and temporal representativity of measurements; and provide recommendations on how to perform in situ measurements.

489 citations

Journal ArticleDOI
TL;DR: Isoscape models of varying quality are available for stable H, C, N, and O isotopes in a range of Earth surface systems, but significant opportunities exist to refine our understanding of biogeochemical cycles and our ability to predict isoscapes through the development of more mechanistic and more comprehensive isoscape model as mentioned in this paper.
Abstract: Isotope ratios of actively cycled elements vary as a function of the biogeochemical processes in which they participate and the conditions under which those processes occur. The resultant spatiotemporal distribution of isotopes in environmental materials can be predicted using models of isotopefractionating processes and data describing environmental conditions across space and time, and it has been termed an isoscape, or isotopic landscape. Analysis of isoscapes and comparison of isoscape predictions with observational data have been used to test biogeochemical models, calculate aerially integrated biogeochemical fluxes based on isotope mass balance, and determine spatial connectivity in biogeochemical, ecological, and anthropological systems. Isoscape models of varying quality are available for stable H, C, N, and O isotopes in a range of Earth surface systems, but significant opportunities exist to refine our understanding of biogeochemical cycles and our ability to predict isoscapes through the development of more mechanistic and more comprehensive isoscape models.

416 citations

Journal ArticleDOI
TL;DR: In this article, the LMDZ-iso general circulation model was used to simulate water-stable isotopes from a midlatitude station and evaluated at different time scales (synoptic to interannual).
Abstract: We present simulations of water-stable isotopes from the LMDZ general circulation model (the LMDZ-iso GCM) and evaluate them at different time scales (synoptic to interannual). LMDZ-iso reproduces reasonably well the spatial and seasonal variations of both delta O-18 and deuterium excess. When nudged with reanalyses, LMDZ-iso is able to capture the synoptic variability of isotopes in winter at a midlatitude station, and the interannual variability in mid and high latitudes is strongly improved. The degree of equilibration between the vapor and the precipitation is strongly sensitive to kinetic effects during rain reevaporation, calling for more synchronous vapor and precipitation measurements. We then evaluate the simulations of two past climates: Last Glacial Maximum (21 ka) and Mid-Holocene (6 ka). A particularity of LMDZ-iso compared to other isotopic GCMs is that it simulates a lower d excess during the LGM over most high-latitude regions, consistent with observations. Finally, we use LMDZ-iso to explore the relationship between precipitation and delta O-18 in the tropics, and we discuss its paleoclimatic implications. We show that the imprint of uniform temperature changes on tropical delta O-18 is weak. Large regional changes in delta O-18 can, however, be associated with dynamical changes of precipitation. Using LMDZ as a test bed for reconstructing past precipitation changes through local delta O-18 records, we show that past tropical precipitation changes can be well reconstructed qualitatively but not quantitatively. Over continents, nonlocal effects make the local reconstruction even less accurate.

315 citations

References
More filters
Journal ArticleDOI
TL;DR: In this article, a global simulation of the stable water isotopes H218O and HD16O as implemented in the hydrological cycle of the ECHAM atmospheric general circulation model is presented.
Abstract: Results are presented of a global simulation of the stable water isotopes H218O and HD16O as implemented in the hydrological cycle of the ECHAM atmospheric general circulation model. The ECHAM model was run under present-day climate conditions at two spatial resolutions (T42,T21), and the simulation results are compared with observations. The high-resolution model (T42) more realistically reproduced the observations, thus demonstrating that an improved representation of advection and orography is critical when modeling the global isotopic water cycle. The deuterium excess (d=δD−8*δ18O) in precipitation offers additional information on climate conditions (e.g., relative humidity and temperature) which prevailed at evaporative sites. Globally, the simulated deuterium excess agrees fairly well with observations showing maxima in the interior of Asia and minima in cold marine regions. However, over Greenland the model failed to show the observed seasonality of the excess and its phase relation to δD reflecting either unrealistic source areas modeled for Greenland precipitation or inadequate description of kinetics in the isotope module. When the coarse resolution model (T21) is forced with observed sea surface temperatures from the period 1979 to 1988, it reproduced the observed weak positive correlation between the isotopic signal and the temperature as well as the weak negative anticorrelation between the isotopic signal and the precipitation. This model simulation further demonstrates that the strongest interannual climate anomaly, the El Nino Southern Oscillation, imprints a strong signal on the water isotopes. In the central Pacific the anticorrelation between the anomalous precipitation and the isotope signal reaches a maximum value of−0.8.

361 citations

Journal ArticleDOI
01 Sep 1984-Nature
TL;DR: In this article, the isotope distribution in precipitation for modern and palaeoconditions is compared using atmospheric general circulation models using isotope cycles, and the results show good agreement between observed and predicted values for modern conditions.
Abstract: H218O and HDO are important climatic tracers largely used to reconstruct continental palaeoclimates. The only thorough way to compare isotopic distributions in precipitation for modern and palaeoconditions is to simulate isotope cycles using atmospheric general circulation models. H218O and HDO cycles incorporated into our atmospheric general circulation model show good agreement between observed and predicted values for modern conditions.

360 citations


"A Review of Antarctic Surface Snow ..." refers background in this paper

  • ...AGCMs equipped with the explicit representation of water-stable isotopes (Joussaume et al. 1984; Jouzel et al. 1987b, 1991; Hoffmann et al. 2000) allow us to disentangle the different factors involved in the spatial (Brown and Simmonds 2004; Schmidt et al....

    [...]

Journal ArticleDOI
TL;DR: A new climatology of Southern Hemisphere (SH) extratropical cyclones was presented by applying a state-of-the-art cyclone tracking scheme to the 6-hourly National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) global reanalyses spanning the period 1958-97.
Abstract: This paper presents a new climatology of Southern Hemisphere (SH) extratropical cyclones. This has been compiled by applying a state-of-the-art cyclone tracking scheme to the 6-hourly National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) global reanalyses spanning the period 1958–97. The results show there to be, on average, between 35 and 38 cyclonic systems per analysis (depending on season), with the greatest density [exceeding 6 × 10−3 cyclones (deg lat)−2] found south of 60°S in all seasons and in the Indian and west Pacific Oceans in autumn and winter. For the most part, there is a net creation of cyclones (i.e., cyclogenesis exceeds cyclolysis) north of about 50°S, and a net destruction to the south of this latitude. Having said this, the most active cyclogenesis takes place south of 45°S. The NCEP–NCAR reanalyses indicate that most SH cyclogenesis occurs at very high latitudes, and the axis of the maximum lies on, or to the south of, 60°S. This...

355 citations


"A Review of Antarctic Surface Snow ..." refers background in this paper

  • ...In this location, it is not the distance from the coast or the elevation that are the main drivers of isotopic depletion, but the distribution along an east–west transect, because moisture is advected from southeast cyclonic activity (Simmonds and Keay 2000)....

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Journal ArticleDOI
TL;DR: In this paper, high resolution records of atmospheric CO2 concentration during the Holocene are obtained from the Dome Concordia and Dronning Maud Land (Antarctica) ice cores.

325 citations


"A Review of Antarctic Surface Snow ..." refers background in this paper

  • ...This result suggests that the accumulation–isotope relationships observed today for the cold conditions of the central plateau may not be extrapolated to warmer conditions, a result that has implications for the mod- eling of the accumulation used for ice core dating (Monnin et al. 2004)....

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