scholarly journals The Isotopic Composition of Present-Day Antarctic Snow in a Lagrangian Atmospheric Simulation*

2007 ◽  
Vol 20 (4) ◽  
pp. 739-756 ◽  
Author(s):  
M. M. Helsen ◽  
R. S. W. Van de Wal ◽  
M. R. Van den Broeke
Keyword(s):  
Isotopic Composition ◽  
General Circulation ◽  
Isotopic Fractionation ◽  
General Circulation Models ◽  
Deuterium Excess ◽  
West Antarctica ◽  
Temperature Relation ◽  
Weather Forecasts ◽  
Spatial Differences ◽  
Antarctic Snow

Abstract The isotopic composition of present-day Antarctic snow is simulated for the period September 1980–August 2002 using a Rayleigh-type isotope distillation model in combination with backward trajectory calculations with 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) data as meteorological input. Observed spatial isotopic gradients are correctly reproduced, especially in West Antarctica and in the coastal areas. However, isotopic depletion of snow on the East Antarctic plateau is underestimated, a problem that is also observed in general circulation models equipped with isotope tracers. The spatial isotope–temperature relation varies strongly, which indicates that this widely used relation is not applicable to all sites and temporal scales. Spatial differences in the seasonal amplitude are identified, with maximum values in the Antarctic interior and hardly any seasonal isotope signature in Marie Byrd Land, West Antarctica. The modeled signature of deuterium excess remains largely preserved during the last phase of transport, though the simulated relation of deuterium excess with δ18O suggests that parameterizations of kinetic isotopic fractionation can be improved.

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

2008 ◽  
Vol 21 (13) ◽  
pp. 3359-3387 ◽  
Author(s):  
V. Masson-Delmotte ◽  
S. Hou ◽  
A. Ekaykin ◽  
J. Jouzel ◽  
A. Aristarain ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
General Circulation ◽  
Deuterium Excess ◽  
Atmospheric Models ◽  
Moisture Advection ◽  
Spatial Coverage ◽  
Antarctic Snow ◽  
Local Variability ◽  
Geographical Characteristics

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.

scholarly journals Isotopic Fractionation at the Base of Polar and Sub-Polar Glaciers

1986 ◽  
Vol 32 (112) ◽  
pp. 475-485 ◽  
Author(s):  
G.S. Boulton ◽  
U. Spring
Keyword(s):  
Isotopic Composition ◽  
Large Scale ◽  
Isotopic Fractionation ◽  
Strong Support ◽  
Sharp Change ◽  
West Antarctica ◽  
Tectonic Structures ◽  
Melt Water ◽  
Glacier Ice ◽  
Hydrological System

AbstractThe melting of ice and the subsequent production of regelation ice from the melt water in a large-scale closed system beneath sub-polar and polar glaciers produces progressive fractionation between the melt water and the regelation ice derived from it. A theory is developed which predicts the change of isotopic composition in regelation ice in a subglacial zone of freezing and in the water from which it is derived. The theory is tested against data from the Byrd Station bore hole in West Antarctica, and applied to explain features of the isotopic composition in several other glaciers where thick sequences of regelation ice have formed.The principal conclusions are:1. Basal isotopic profiles can be used to reconstruct important features of a glacier’s hydrological system.2. Isotopic profiles in basal regelation ice do not simply reflect isotopic characteristics of ancient atmospheres but also, by using the theory, some of the isotopic characteristics of the normal glacier ice which was destroyed by melting and subsequently produced regelation ice can be reconstructed. Basal regelation ice at Byrd Station reflects an original ice source isotopically colder than the overlying normal ice, and may have formed during the penultimate glacial period, equivalent to stage 6 of the oceanic record.3. The subglacially derived debris typically found in basal regelation ice gives a complex strain response to a changing pattern of stresses produced by flow over an irregular subjacent bed. Thus, complex tectonic structures in this ice produce highly variable isotopic profiles. However, its gross isotopic characteristics can still be used to reconstruct some of its history. A sharp change in isotopic values tends to occur at the upper limit of basal regelation ice, the nature of which depends on the style and thickness of tectonic disturbance.4. Isotopic profiles in basal ice can be used to distinguish normal glacier ice from regelation ice, and give strong support to the view that regelation is the major process by which debris is incorporated into the base of a glacier.

scholarly journals Modelling the isotopic composition of snow using backward trajectories: a particular precipitation event in Dronning Maud Land, Antarctica

2004 ◽  
Vol 39 ◽  
pp. 293-299 ◽  
Author(s):  
Michiel M. Helsen ◽  
Roderik S. W. Van De Wal ◽  
Michiel R. Van Den Broeke ◽  
Erik R. Th. Kerstel ◽  
Valérie Masson-Delmotte ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Water Vapour ◽  
General Circulation ◽  
General Circulation Models ◽  
Precipitation Event ◽  
Backward Trajectories ◽  
Specific Accumulation ◽  
Transport Path ◽  
History Of ◽  
Dronning Maud Land

AbstractWe consider a specific accumulation event that occurred in January 2002 in western Dronning Maud Land, Antarctica. Snow samples were obtained a few days after accumulation. We combine meteorological analyses and isotopic modelling to describe the isotopic composition of moisture during transport. Backward trajectories were calculated, based on European Centre for Medium-Range Weather Forecasts operational archive data so that the history of the air parcels transporting water vapour to the accumulation site could be reconstructed. This trajectory study showed that the air masses were not (super)saturated along most of the transport path, which is in contrast with assumptions in Lagrangian fractionation models and probably true for most precipitation events in Antarctica. The modelled fractionation along the trajectories was too limited to explain the measured isotopic content of the snow. It is shown that the observed isotopic composition of precipitation resulted from fractionation of initially more depleted water. This lower initial isotopic composition of water vapour might result from atmospheric mixing with more depleted air along the trajectory or from earlier condensation cycles, not captured by the trajectories. This is in accordance with isotope fields resulting from general circulation models, indicating a gradient in isotopic composition from the Equator to Antarctica.

scholarly journals Three-year monitoring of stable isotopes of precipitation at Concordia Station, East Antarctica

2016 ◽  
Author(s):  
Barbara Stenni ◽  
Claudio Scarchilli ◽  
Valerie Masson-Delmotte ◽  
Elisabeth Schlosser ◽  
Virginia Ciardini ◽  
...  
Keyword(s):  
Stable Isotopes ◽  
Isotopic Composition ◽  
Air Temperature ◽  
General Circulation ◽  
Daily Precipitation ◽  
Circulation Model ◽  
Ice Cores ◽  
Condensation Temperature ◽  
Deuterium Excess ◽  
Medium Range Weather Forecast

Abstract. Past temperature reconstructions from Antarctic ice cores require a good quantification and understanding of the relationship between snow isotopic composition and 2&thninsp;m air or inversion (condensation) temperature. Here, we focus on the French-Italian Concordia Station, central East Antarctic plateau, where the European Project for Ice Coring in Antarctica (EPICA) Dome C ice cores were drilled. We provide a multi-year record of daily precipitation types identified from crystal morphologies, daily precipitation amounts, and isotopic composition. Our sampling period (2008–2010) encompasses a warmer year (2009, +1.6 °C with respect to 2&thninsp;m air temperature period average), with larger total precipitation and snowfall amounts (14 %, 76 % above average, respectively), and a colder and drier year (2010, −1.4 °C, 4 % below average, respectively) with larger diamond dust amounts (49 % above average). Relationships between local meteorological data and precipitation isotopic composition are investigated at daily, monthly and inter-annual scale, and for the different types of precipitation. Water stable isotopes are more closely related to 2 m air temperature than to inversion temperature at all time scales (e.g. R2 = 0.63 and 0.44, respectively for daily values). The slope of the temporal relationship between daily d18O and 2 m air temperature is approximately two times smaller (0.49 ‰/°C) than the average Antarctic spatial (0.8 ‰/°C) relationship initially used for the interpretation of EPICA Dome C records. In accordance to results from precipitation monitoring at Vostok and Dome F, deuterium excess is anti-correlated with δ18O at daily and monthly scales, reaching maximum values in winter. Hoar frost precipitation samples have a specific fingerprint with more depleted d18O (about 5 ‰ below average) and higher deuterium excess (about 8 ‰ above average) values than other precipitation types. These datasets provide a basis for comparison with shallow ice core records, to investigate post-deposition effects. A preliminary comparison between observations and precipitation from the European Centre for Medium-Range Weather Forecast (ECMWF) re-analysis and the simulated water stable isotopes from the Laboratoire de Météorologie Dynamique Zoom atmospheric general circulation model (LMDZiso), shows that models do correctly capture the amount of precipitation as well as more than 50 % of the variance of the observed δ18O, driven by large scale weather patterns. Despite a warm bias and an underestimation of the variance in water stable isotopes, LMDZiso correctly captures these relationships between δ18O, 2 m air temperature and deuterium excess. Our dataset is therefore available for further in depth model evaluation at the synoptic scale.

Spatial patterns of multi-centennial temperature trend in Antarctica over 0-1000 CE: insights from ice core records and modeling

2021 ◽  
Author(s):  
Zhiqiang Lyu ◽  
Hugues Goosse ◽  
Quentin Dalaiden
Keyword(s):  
General Circulation ◽  
Climate Models ◽  
Ice Core ◽  
High Sensitivity ◽  
General Circulation Models ◽  
Temperature Trend ◽  
East Antarctica ◽  
West Antarctica ◽  
Amundsen Sea ◽  
Ice Core Records

<p>Recent Antarctic surface climate change has been characterized by greater warming trends in West Antarctica than in East Antarctica. Although the changes over recent decades are well studied, the short instrumental record limits our ability to determine if such asymmetric patterns are common for Antarctica and the processes at their origin. Here, we will focus on the years 0-1000 CE as some ice core records display very contrasted trends during this period. Furthermore, the climate models are unable to reproduce the warming displayed in some reconstructions from 1 to 500 CE over East Antarctica. In order to understand the origin of these apparent incompatibilities and investigate the effect of proxy selection on regional reconstructions over 0-1000 CE, we performed several offline data assimilation experiments based on different groups of d<sup>18</sup>O records and the isotope-enabled general circulation models (iCESM). When assimilating different d18O data sets, large differences appear in the pattern of temperature trend over 0-500 CE, but the patterns over 500-1000 CE are more consistent among the various experiments. This implies that the spatial pattern of temperature trend over 0-500 CE is still uncertain because of this high sensitivity on the choice of the proxies to constrain the model results, while the pattern over 500-1000 is more robust, with the greater cooling over West Antarctica than East Antarctica. This pattern over 500-1000 CE relates to the intensifying of the low pressure centered in the Amundsen Sea, which induces enhanced southerly flow through most of WAIS.</p>

High-resolution isotopic simulations from ECHAM6-wiso nudged with ERA5 reanalyses: new products for isotopic model-data comparisons

2020 ◽  
Author(s):  
Alexandre Cauquoin ◽  
Martin Werner
Keyword(s):  
General Circulation ◽  
Ice Cores ◽  
General Circulation Models ◽  
Global Network ◽  
Climate Data ◽  
Isotopic Data ◽  
Surrounding Water ◽  
Weather Forecasts ◽  
The Impact ◽  
Water Isotope

<p>For several decades, the comparison of climate data with results from water isotope-enabled Atmosphere General Circulation Models (AGCMs) significantly helped to a better understanding of the processes ruling the water cycle, which is one of the main drivers of the climate variability. For the modern period, the use of AGCMs nudged with weather forecasts reanalyses is a powerful way to obtain model outputs under the same weather conditions than at the sampling time of the observations.</p><p>Here we present new isotopic simulations results from ECHAM6-wiso [1] nudged with the last reanalyses dataset from the European Centre for Medium-Range Weather Forecasts (ECMWF), ERA5 [2], at different spatial resolutions over the period 1979-2018. Model results are evaluated against isotopic data compilations, including GNIP (Global Network of Isotopes in Precipitation [3]), speleothems [4], ice cores datasets and water vapor measurements. To quantify the impact of these reanalyses on our simulations, we also performed nudged simulations with the previous model version ECHAM5-wiso [5] by using ERA5 data and its predecessor ERA-Interim [6].</p><p>These new simulation products could be a useful contribution to the isotopic data community for the interpretation of their water isotope records and for the exploration of the mechanisms controlling the variability of the surrounding water isotopic composition.</p><p> </p><p>[1] Cauquoin et al., Clim. Past, <strong>15</strong>, 1913–1937, https://doi.org/10.5194/cp-15-1913-2019, 2019.</p><p>[2] Copernicus Climate Change Service (C3S), 2017.</p><p>[3] IAEA, the GNIP Database, available at: https://nucleus.iaea.org/wiser.</p><p>[4] Comas-Bru et al., Clim. Past, <strong>15</strong>, 1557–1579, https://doi.org/10.5194/cp-15-1557-2019, 2019.</p><p>[5] Werner et al., Geosci. Model Dev., <strong>9</strong>, 647–670, https://doi.org/10.5194/gmd-9-647-2016, 2016.</p><p>[6] Dee et al., Q. J. R. Meteorol. Soc., <strong>137</strong>, 553–597, https://doi.org/10.1002/qj.828, 2011.</p>

scholarly journals Isotopic Fractionation at the Base of Polar and Sub-Polar Glaciers

1986 ◽  
Vol 32 (112) ◽  
pp. 475-485 ◽  
Author(s):  
G.S. Boulton ◽  
U. Spring
Keyword(s):  
Isotopic Composition ◽  
Large Scale ◽  
Isotopic Fractionation ◽  
Strong Support ◽  
Sharp Change ◽  
West Antarctica ◽  
Tectonic Structures ◽  
Melt Water ◽  
Glacier Ice ◽  
Hydrological System

AbstractThe melting of ice and the subsequent production of regelation ice from the melt water in a large-scale closed system beneath sub-polar and polar glaciers produces progressive fractionation between the melt water and the regelation ice derived from it. A theory is developed which predicts the change of isotopic composition in regelation ice in a subglacial zone of freezing and in the water from which it is derived. The theory is tested against data from the Byrd Station bore hole in West Antarctica, and applied to explain features of the isotopic composition in several other glaciers where thick sequences of regelation ice have formed.The principal conclusions are:1. Basal isotopic profiles can be used to reconstruct important features of a glacier’s hydrological system.2. Isotopic profiles in basal regelation ice do not simply reflect isotopic characteristics of ancient atmospheres but also, by using the theory, some of the isotopic characteristics of the normal glacier ice which was destroyed by melting and subsequently produced regelation ice can be reconstructed. Basal regelation ice at Byrd Station reflects an original ice source isotopically colder than the overlying normal ice, and may have formed during the penultimate glacial period, equivalent to stage 6 of the oceanic record.3. The subglacially derived debris typically found in basal regelation ice gives a complex strain response to a changing pattern of stresses produced by flow over an irregular subjacent bed. Thus, complex tectonic structures in this ice produce highly variable isotopic profiles. However, its gross isotopic characteristics can still be used to reconstruct some of its history. A sharp change in isotopic values tends to occur at the upper limit of basal regelation ice, the nature of which depends on the style and thickness of tectonic disturbance.4. Isotopic profiles in basal ice can be used to distinguish normal glacier ice from regelation ice, and give strong support to the view that regelation is the major process by which debris is incorporated into the base of a glacier.

scholarly journals The isotopic composition of water vapour and precipitation in Ivittuut, Southern Greenland

2013 ◽  
Vol 13 (11) ◽  
pp. 30521-30574 ◽  
Author(s):  
J.-L. Bonne ◽  
V. Masson-Delmotte ◽  
O. Cattani ◽  
M. Delmotte ◽  
C. Risi ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Isotopic Composition ◽  
Water Vapour ◽  
Seasonal Variations ◽  
General Circulation ◽  
Deuterium Excess ◽  
Local Surface ◽  
Long Distance ◽  
Atlantic Sector ◽  
Moisture Sources

Abstract. Since September 2011, a Wavelength-Scanned Cavity Ringdown Spectroscopy analyzer has been remotely operated in Ivittuut, southern Greenland, providing the first continuous record of surface water vapour isotopic composition (δ18O, δD) in South Greenland and the first record including the winter season in Greenland. This record depicts small summer diurnal variations. Measurements of precipitation isotopic composition suggest equilibrium between surface vapour and precipitation. The vapour data show large synoptic and seasonal variations corresponding to shifts in moisture sources estimated using a quantitative moisture source diagnostic. The arrival of low pressure systems towards south Greenland leads to δ18O enrichment (+5‰) and deuterium excess depletion (−15‰), coupled with moisture sources shifts. Monthly δ18O is minimum in November–December and maximum in June–July, with a seasonal amplitude of ~10‰. The strong correlation between δ18O and the logarithm of local surface humidity is consistent with Rayleigh distillation processes. The relationship with local surface air temperature is associated with a slope of ~0.4‰ °C−1. During the summer 2012 heat waves, the observations display a divergence between δ18O and local climate variables, probably due to the isotopic depletion associated with long distance transport from subtropical moisture sources. Monthly deuterium excess is minimum in May–June and maximum in November, with a seasonal amplitude of 20‰. It is anti-correlated with δ18O, and correlated with local surface relative humidity (at the station) as well as surface relative humidity in a North Atlantic sector, south of Greenland and Iceland. While synoptic and seasonal variations are well represented by the Atmospheric General Circulation Model LMDZiso for Ivittuut δ18O, the model does not capture the magnitude of these variations for deuterium excess.

scholarly journals OpenIFS@home version 1: a citizen science project for ensemble weather and climate forecasting

2020 ◽  
Author(s):  
Sarah Sparrow ◽  
Andrew Bowery ◽  
Glenn D. Carver ◽  
Marcus O. Köhler ◽  
Pirkka Ollinaho ◽  
...  
Keyword(s):  
Citizen Science ◽  
General Circulation ◽  
Weather Forecast ◽  
Forecast Model ◽  
General Circulation Models ◽  
Operational Environment ◽  
Computing Systems ◽  
Weather Forecasts ◽  
Operational Forecasts ◽  
Weather Forecast Model

Abstract. Weather forecasts rely heavily on general circulation models of the atmosphere and other components of the Earth system. National meteorological and hydrological services and intergovernmental organisations, such as the European Centre for Medium-Range Weather Forecasts (ECMWF), provide routine operational forecasts on a range of spatio-temporal scales, by running these models in high resolution on state-of-the-art high-performance computing systems. Such operational forecasts are very demanding in terms of computing resources. To facilitate the use of a weather forecast model for research and training purposes outside the operational environment, ECMWF provides a portable version of its numerical weather forecast model, OpenIFS, for use by universities and other research institutes on their own computing systems. In this paper, we describe a new project (OpenIFS@home) that combines OpenIFS with a citizen science approach to involve the general public in helping conduct scientific experiments. Volunteers from across the world can run OpenIFS@home on their computers at home and the results of these simulations can be combined into large forecast ensembles. The infrastructure of such distributed computing experiments is based on our experience and expertise with the climateprediction.net and weather@home systems. In order to validate this first use of OpenIFS in a volunteer computing framework, we present results from ensembles of forecast simulations of tropical cyclone Karl from September 2016, studied during the NAWDEX field campaign. This cyclone underwent extratropical transition and intensified in mid-latitudes to give rise to an intense jet-streak near Scotland and heavy rainfall over Norway. For the validation we use a two thousand member ensemble of OpenIFS run on the OpenIFS@home volunteer framework and a smaller ensemble of the size of operational forecasts using ECMWF’s forecast model in 2016 run on the ECMWF supercomputer with the same horizontal resolution as OpenIFS@home. We present ensemble statistics that illustrate the reliability and accuracy of the OpenIFS@home forecasts as well as discussing the use of large ensembles in the context of forecasting extreme events.

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