40838
2016
2019
eng
17
500
postprint
1
2019-01-17
2019-01-17
--
Regional climate signal vs. local noise
In low-accumulation regions, the reliability of delta O-18-derived temperature signals from ice cores within the Holocene is unclear, primarily due to the small climate changes relative to the intrinsic noise of the isotopic signal. In order to learn about the representativity of single ice cores and to optimise future ice-core-based climate reconstructions, we studied the stable-water isotope composition of firn at Kohnen Station, Dronning Maud Land, Antarctica. Analysing delta O-18 in two 50m long snow trenches allowed us to create an unprecedented, two-dimensional image characterising the isotopic variations from the centimetre to the 100-metre scale. Our results show seasonal layering of the isotopic composition but also high horizontal isotopic variability caused by local stratigraphic noise. Based on the horizontal and vertical structure of the isotopic variations, we derive a statistical noise model which successfully explains the trench data. The model further allows one to determine an upper bound for the reliability of climate reconstructions conducted in our study region at seasonal to annual resolution, depending on the number and the spacing of the cores taken.
Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
a two-dimensional view of water isotopes in Antarctic firn at Kohnen Station, Dronning Maud Land
10.25932/publishup-40838
urn:nbn:de:kobv:517-opus4-408385
1866-8372
online registration
Climate of the Past 12 (2016), pp. 1565-1581 DOI: 10.5194/cp-12-1565-2016
CC-BY - Namensnennung 4.0 International
Thomas Münch
Sepp Kipfstuhl
Johannes Freitag
Hanno Meyer
Thomas Laepple
Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
500
eng
uncontrolled
ice-core records
eng
uncontrolled
past 2 kyr
eng
uncontrolled
temperature variability
eng
uncontrolled
accumulation rates
eng
uncontrolled
East Antarctica
eng
uncontrolled
stable-isotopes
eng
uncontrolled
surface snow
eng
uncontrolled
time-series
eng
uncontrolled
diffusion
eng
uncontrolled
Greenland
Geowissenschaften
open_access
Mathematisch-Naturwissenschaftliche Fakultät
Referiert
Open Access
Copernicus
Universität Potsdam
https://publishup.uni-potsdam.de/files/40838/pmnr500.pdf
45764
2016
2016
eng
1565
1581
17
12
article
Copernicus
Göttingen
1
--
--
--
Regional climate signal vs. local noise: a two-dimensional view of water isotopes in Antarctic firn at Kohnen Station, Dronning Maud Land
In low-accumulation regions, the reliability of delta O-18-derived temperature signals from ice cores within the Holocene is unclear, primarily due to the small climate changes relative to the intrinsic noise of the isotopic signal. In order to learn about the representativity of single ice cores and to optimise future ice-core-based climate reconstructions, we studied the stable-water isotope composition of firn at Kohnen Station, Dronning Maud Land, Antarctica. Analysing delta O-18 in two 50m long snow trenches allowed us to create an unprecedented, two-dimensional image characterising the isotopic variations from the centimetre to the 100-metre scale. Our results show seasonal layering of the isotopic composition but also high horizontal isotopic variability caused by local stratigraphic noise. Based on the horizontal and vertical structure of the isotopic variations, we derive a statistical noise model which successfully explains the trench data. The model further allows one to determine an upper bound for the reliability of climate reconstructions conducted in our study region at seasonal to annual resolution, depending on the number and the spacing of the cores taken.
Climate of the past : an interactive open access journal of the European Geosciences Union
10.5194/cp-12-1565-2016
1814-9324
1814-9332
wos2016:2019
WOS:000381275100006
Munch, T (reprint author), Alfred Wegener Inst Helmholtz Ctr Polar & Marine, Telegrafenberg A43, D-14473 Potsdam, Germany.; Munch, T (reprint author), Univ Potsdam, Inst Phys & Astron, Karl Liebknecht Str 24-25, D-14476 Potsdam, Germany., thomas.muench@awi.de
Initiative and Networking Fund of the Helmholtz Association [VG-NH900]
importub
2020-03-22T21:15:01+00:00
filename=package.tar
c908bdd3c6c6c9bedd8d32f4cb8d3906
Thomas Münch
Sepp Kipfstuhl
Johannes Freitag
Hanno Meyer
Thomas Laepple
Institut für Physik und Astronomie
Referiert
Import
44870
2016
2016
eng
1849
1860
12
121
article
American Geophysical Union
Washington
1
--
--
--
Layering of surface snow and firn at Kohnen Station, Antarctica: Noise or seasonal signal?
The density of firn is an important property for monitoring and modeling the ice sheets as well as to model the pore close-off and thus to interpret ice core-based greenhouse gas records. One feature, which is still in debate, is the potential existence of an annual cycle of firn density in low-accumulation regions. Several studies describe or assume seasonally successive density layers, horizontally evenly distributed, as seen in radar data. On the other hand, high-resolution density measurements on firn cores in Antarctica and Greenland show no clear seasonal cycle in the top few meters. A major caveat of most existing snow-pit and firn-core-based studies is that they represent one vertical profile from a laterally heterogeneous density field. To overcome this, we created an extensive data set of horizontal and vertical density data at Kohnen Station, Dronning Maud Land, on the East Antarctic Plateau. We drilled and analyzed three 90m long firn cores as well as 143 one-meter-long vertical profiles from two elongated snow trenches to obtain a two-dimensional view of the density variations. The analysis of the 45m wide and 1m deep density fields reveals a seasonal cycle in density. However, the seasonality is overprinted by strong stratigraphic noise, making it invisible when analyzing single firn cores. Our density data set extends the view from the local ice core perspective to a hundred meter scale and thus supports linking spatially integrating methods such as radar and seismic studies to ice and firn cores.
Journal of geophysical research : Earth surface
10.1002/2016JF003919
2169-9003
2169-9011
wos2016:2019
WOS:000392830200013
Laepple, T (reprint author), Helmholtz Ctr Polar & Marine Res, Alfred Wegener Inst, Potsdam, Germany., tlaepple@awi.de
German Science Foundation [HO-5036/1-1]; Initiative and Networking Fund of the Helmholtz Association [VG-NH900]
importub
2020-03-22T13:47:01+00:00
filename=package.tar
bad69c395eaf2d59cacb2cf9a3029f55
Thomas Laepple
Maria Hörhold
Thomas Münch
Johannes Freitag
Anna Wegner
Sepp Kipfstuhl
Institut für Physik und Astronomie
Referiert
Import
41876
2017
2019
eng
14
662
postprint
1
2019-03-01
2019-03-01
--
Constraints on post-depositional isotope modifications in East Antarctic firn from analysing temporal changes of isotope profiles
The isotopic composition of water in ice sheets is extensively used to infer past climate changes. In low-accumulation regions their interpretation is, however, challenged by poorly constrained effects that may influence the initial isotope signal during and after deposition of the snow. This is reflected in snow-pit isotope data from Kohnen Station, Antarctica, which exhibit a seasonal cycle but also strong interannual variations that contradict local temperature observations. These inconsistencies persist even after averaging many profiles and are thus not explained by local stratigraphic noise. Previous studies have suggested that post-depositional processes may significantly influence the isotopic composition of East Antarctic firn. Here, we investigate the importance of post-depositional processes within the open-porous firn (greater than or similar to 10 cm depth) at Kohnen Station by separating spatial from temporal variability. To this end, we analyse 22 isotope profiles obtained from two snow trenches and examine the temporal isotope modifications by comparing the new data with published trench data extracted 2 years earlier. The initial isotope profiles undergo changes over time due to downward advection, firn diffusion and densification in magnitudes consistent with independent estimates. Beyond that, we find further modifications of the original isotope record to be unlikely or small in magnitude (<< 1 parts per thousand RMSD). These results show that the discrepancy between local temperatures and isotopes most likely originates from spatially coherent processes prior to or during deposition, such as precipitation intermittency or systematic isotope modifications acting on drifting or loose surface snow.
Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
10.25932/publishup-41876
urn:nbn:de:kobv:517-opus4-418763
1866-8372
online registration
The Cryosphere 11 (2017), pp. 2175–2188 DOI 10.5194/tc-11-2175-2017
false
true
CC-BY - Namensnennung 4.0 International
Thomas Münch
Sepp Kipfstuhl
Johannes Freitag
Hanno Meyer
Thomas Laepple
Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
662
eng
uncontrolled
Dronning Maud Land
eng
uncontrolled
near-surface snow
eng
uncontrolled
Ice core records
eng
uncontrolled
Kohnen Station
eng
uncontrolled
stable isotopes
eng
uncontrolled
water isotopes
eng
uncontrolled
polar firn
eng
uncontrolled
climate
eng
uncontrolled
diffusion
eng
uncontrolled
precipitation
Geografie, Reisen
open_access
Mathematisch-Naturwissenschaftliche Fakultät
Referiert
Open Access
Copernicus
Universität Potsdam
https://publishup.uni-potsdam.de/files/41876/pmnr662.pdf
53903
2018
2018
eng
169
187
19
1
12
article
Copernicus
Göttingen
1
--
--
--
On the similarity and apparent cycles of isotopic variations in East Antarctic snow pits
Stable isotope ratios delta O-18 and delta D in polar ice provide a wealth of information about past climate evolution. Snow-pit studies allow us to relate observed weather and climate conditions to the measured isotope variations in the snow. They therefore offer the possibility to test our understanding of how isotope signals are formed and stored in firn and ice. As delta O-18 and delta D in the snowfall are strongly correlated to air temperature, isotopes in the near-surface snow are thought to record the seasonal cycle at a given site. Accordingly, the number of seasonal cycles observed over a given depth should depend on the accumulation rate of snow. However, snow-pit studies from different accumulation conditions in East Antarctica reported similar isotopic variability and comparable apparent cycles in the delta O-18 and delta D profiles with typical wavelengths of similar to 20 cm. These observations are unexpected as the accumulation rates strongly differ between the sites, ranging from 20 to 80mmw.e.yr(-1) (similar to 6-21 cm of snow per year). Various mechanisms have been proposed to explain the isotopic variations individually at each site; however, none of these are consistent with the similarity of the different profiles independent of the local accumulation conditions. Here, we systematically analyse the properties and origins of delta O-18 and delta D variations in high-resolution firn profiles from eight East Antarctic sites. First, we confirm the suggested cycle length (mean distance between peaks) of similar to 20 cm by counting the isotopic maxima. Spectral analysis further shows a strong similarity between the sites but indicates no dominant periodic features. Furthermore, the appar-ent cycle length increases with depth for most East Antarctic sites, which is inconsistent with burial and compression of a regular seasonal cycle. We show that these results can be explained by isotopic diffusion acting on a noise-dominated isotope signal. The firn diffusion length is rather stable across the Antarctic Plateau and thus leads to similar power spectral densities of the isotopic variations. This in turn implies a similar distance between isotopic maxima in the firn profiles. Our results explain a large set of observations discussed in the literature, providing a simple explanation for the interpretation of apparent cycles in shallow isotope records, without invoking complex mechanisms. Finally, the results underline previous suggestions that isotope signals in single ice cores from low-accumulation regions have a small signal-to-noise ratio and thus likely do not allow the reconstruction of interannual to decadal climate variations.
The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union
10.5194/tc-12-169-2018
1994-0416
1994-0424
wos:2018
WOS:000422885300001
Laepple, T (reprint author), Helmholtz Ctr Polar & Marine Res, Alfred Wegener Inst, Telegrafenberg A43, D-14473 Potsdam, Germany., thomas.laepple@awi.de
Initiative and Networking Fund of the Helmholtz Association grant Seventh Framework Programme (FP7)/RC grant [306045]; ERC under the
2022-02-14T16:35:01+00:00
sword
importub
filename=package.tar
3de40b27e8c44fabf3d0638b15e87980
<a href="https://doi.org/10.25932/publishup-44605">Zweitveröffentlichung in der Schriftenreihe Postprints der Universität Potsdam : Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe ; 932 </a>
false
true
CC-BY - Namensnennung 4.0 International
Thomas Laepple
Thomas Münch
Mathieu Casado
Maria Hoerhold
Amaelle Landais
Sepp Kipfstuhl
Geografie, Reisen
Institut für Geowissenschaften
Import
53562
2018
2018
eng
356
359
16
7692
554
article
Nature Publ. Group
London
1
2018-02-05
2018-02-05
--
Global patterns of declining temperature variability from the Last Glacial Maximum to the Holocene
Changes in climate variability are as important for society to address as are changes in mean climate(1). Contrasting temperature variability during the Last Glacial Maximum and the Holocene can provide insights into the relationship between the mean state of the climate and its variability(2,3). However, although glacial-interglacial changes in variability have been quantified for Greenland(2), a global view remains elusive. Here we use a network of marine and terrestrial temperature proxies to show that temperature variability decreased globally by a factor of four as the climate warmed by 3-8 degrees Celsius from the Last Glacial Maximum (around 21,000 years ago) to the Holocene epoch (the past 11,500 years). This decrease had a clear zonal pattern, with little change in the tropics (by a factor of only 1.6-2.8) and greater change in the mid-latitudes of both hemispheres (by a factor of 3.3-14). By contrast, Greenland ice-core records show a reduction in temperature variability by a factor of 73, suggesting influences beyond local temperature or a decoupling of atmospheric and global surface temperature variability for Greenland. The overall pattern of reduced variability can be explained by changes in the meridional temperature gradient, a mechanism that points to further decreases in temperature variability in a warmer future.
Nature : the international weekly journal of science
10.1038/nature25454
29400701
0028-0836
1476-4687
wos:2018
WOS:000424996300037
Rehfeld, K (reprint author), Alfred Wegener Inst, Helmholtz Ctr Polar & Marine Res, Telegrafenberg A43, D-14473 Potsdam, Germany.; Rehfeld, K (reprint author), British Antarctic Survey, Madingley Rd, Cambridge CB3 0ET, England., krehfeld@awi.de
Initiative and Networking Fund of the Helmholtz Association [VG-900NH]; German Science Foundation (DFG)German Research Foundation (DFG) [RE 3994/1-1]; European Research Council (ERC) under the European UnionEuropean Research Council (ERC) [716092]; CEAFrench Atomic Energy Commission; CNRSCentre National de la Recherche Scientifique (CNRS)
2022-01-24T07:27:53+00:00
sword
importub
filename=package.tar
322fb244a5f71eaa86177b01675a554a
false
true
Kira Rehfeld
Thomas Münch
Sze Ling Ho
Thomas Laepple
Geowissenschaften
Institut für Geowissenschaften
Referiert
Import
Green Open-Access
44605
2018
2020
eng
169
187
21
932
postprint
1
2020-06-02
2020-06-02
--
On the similarity and apparent cycles of isotopic variations in East Antarctic snow pits
Stable isotope ratios delta O-18 and delta D in polar ice provide a wealth of information about past climate evolution. Snow-pit studies allow us to relate observed weather and climate conditions to the measured isotope variations in the snow. They therefore offer the possibility to test our understanding of how isotope signals are formed and stored in firn and ice. As delta O-18 and delta D in the snowfall are strongly correlated to air temperature, isotopes in the near-surface snow are thought to record the seasonal cycle at a given site. Accordingly, the number of seasonal cycles observed over a given depth should depend on the accumulation rate of snow. However, snow-pit studies from different accumulation conditions in East Antarctica reported similar isotopic variability and comparable apparent cycles in the delta O-18 and delta D profiles with typical wavelengths of similar to 20 cm. These observations are unexpected as the accumulation rates strongly differ between the sites, ranging from 20 to 80mmw.e.yr(-1) (similar to 6-21 cm of snow per year). Various mechanisms have been proposed to explain the isotopic variations individually at each site; however, none of these are consistent with the similarity of the different profiles independent of the local accumulation conditions.
Here, we systematically analyse the properties and origins of delta O-18 and delta D variations in high-resolution firn profiles from eight East Antarctic sites. First, we confirm the suggested cycle length (mean distance between peaks) of similar to 20 cm by counting the isotopic maxima. Spectral analysis further shows a strong similarity between the sites but indicates no dominant periodic features. Furthermore, the appar-ent cycle length increases with depth for most East Antarctic sites, which is inconsistent with burial and compression of a regular seasonal cycle. We show that these results can be explained by isotopic diffusion acting on a noise-dominated isotope signal. The firn diffusion length is rather stable across the Antarctic Plateau and thus leads to similar power spectral densities of the isotopic variations. This in turn implies a similar distance between isotopic maxima in the firn profiles. Our results explain a large set of observations discussed in the literature, providing a simple explanation for the interpretation of apparent cycles in shallow isotope records, without invoking complex mechanisms. Finally, the results underline previous suggestions that isotope signals in single ice cores from low-accumulation regions have a small signal-to-noise ratio and thus likely do not allow the reconstruction of interannual to decadal climate variations.
Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe
10.25932/publishup-44605
urn:nbn:de:kobv:517-opus4-446052
1866-8372
The Cryosphere 12 (2018) 169–187 DOI: 10.5194/tc-12-169-2018
<a href="http://publishup.uni-potsdam.de/53903">Bibliographieeintrag der Originalveröffentlichung/Quelle</a>
CC-BY - Namensnennung 4.0 International
Thomas Laepple
Thomas Münch
Mathieu Casado
Maria Hoerhold
Amaelle Landais
Sepp Kipfstuhl
Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
932
eng
uncontrolled
Dronning-Maud-Land
eng
uncontrolled
ice-core
eng
uncontrolled
climate variability
eng
uncontrolled
surface snow
eng
uncontrolled
stable-isotopes
eng
uncontrolled
water-isotopes
eng
uncontrolled
oxygen-isotope
eng
uncontrolled
south-pole
eng
uncontrolled
athmospheric circulation
eng
uncontrolled
mathematical-analysis
Geografie, Reisen
open_access
Mathematisch-Naturwissenschaftliche Fakultät
Referiert
Open Access
Universität Potsdam
https://publishup.uni-potsdam.de/files/44605/pmnr932.pdf
52876
2018
2018
eng
1745
1766
22
5
12
article
Copernicus
Göttingen
1
2018-05-24
2018-05-24
--
Archival processes of the water stable isotope signal in East Antarctic ice cores
The oldest ice core records are obtained from the East Antarctic Plateau. Water isotopes are key proxies to reconstructing past climatic conditions over the ice sheet and at the evaporation source. The accuracy of climate reconstructions depends on knowledge of all processes affecting water vapour, precipitation and snow isotopic compositions. Fractionation processes are well understood and can be integrated in trajectory-based Rayleigh distillation and isotope-enabled climate models. However, a quantitative understanding of processes potentially altering snow isotopic composition after deposition is still missing. In low-accumulation sites, such as those found in East Antarctica, these poorly constrained processes are likely to play a significant role and limit the interpretability of an ice core's isotopic composition.
By combining observations of isotopic composition in vapour, precipitation, surface snow and buried snow from Dome C, a deep ice core site on the East Antarctic Plateau, we found indications of a seasonal impact of metamorphism on the surface snow isotopic signal when compared to the initial precipitation. Particularly in summer, exchanges of water molecules between vapour and snow are driven by the diurnal sublimation-condensation cycles. Overall, we observe in between precipitation events modification of the surface snow isotopic composition. Using high-resolution water isotopic composition profiles from snow pits at five Antarctic sites with different accumulation rates, we identified common patterns which cannot be attributed to the seasonal variability of precipitation. These differences in the precipitation, surface snow and buried snow isotopic composition provide evidence of post-deposition processes affecting ice core records in low-accumulation areas.
The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union
10.5194/tc-12-1745-2018
1994-0416
1994-0424
wos:2018
WOS:000433005400002
Casado, M (reprint author), CEA CNRS UVSQ UPS, Lab Sci Climat & Environm IPSL, UMR 8212, Gif Sur Yvette, France.; Casado, M (reprint author), Univ Grenoble Alpes, CNRS, LIPHY, F-38000 Grenoble, France., mathieu.casado@gmail.com
Programme (FP7)/RC grant [306045]; Initiative and Networking Fund of the Helmholtz Association Grant [VG-NH900]; LGGE; LIPHY
2021-11-30T08:51:58+00:00
sword
importub
filename=package.tar
00053b082b6a5226149448b531bb306c
Casado, Mathieu
<a href="https://doi.org/10.25932/publishup-42705">Zweitveröffentlichung in der Schriftenreihe Postprints der Universität Potsdam : Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe ; 716 </a>
CC-BY - Namensnennung 4.0 International
Mathieu Casado
Amaelle Landais
Ghislain Picard
Thomas Münch
Thomas Laepple
Barbara Stenni
Giuliano Dreossi
Alexey Ekaykin
Laurent Arnaud
Christophe Genthon
Alexandra Touzeau
Valerie Masson-Delmotte
Jean Jouzel
Geowissenschaften
Institut für Geowissenschaften
Referiert
Import
Gold Open-Access
DOAJ gelistet
51425
2018
2018
eng
2053
2070
18
12
14
article
Copernicus Gesellschaft mbH
Göttingen
1
2018-12-20
2018-12-20
--
What climate signal is contained in decadal- to centennial-scale isotope variations from Antarctic ice cores?
Ice-core-based records of isotopic composition are a proxy for past temperatures and can thus provide information on polar climate variability over a large range of timescales. However, individual isotope records are affected by a multitude of processes that may mask the true temperature variability. The relative magnitude of climate and non-climate contributions is expected to vary as a function of timescale, and thus it is crucial to determine those temporal scales on which the actual signal dominates the noise. At present, there are no reliable estimates of this timescale dependence of the signal-to-noise ratio (SNR). Here, we present a simple method that applies spectral analyses to stable-isotope data from multiple cores to estimate the SNR, and the signal and noise variability, as a function of timescale. The method builds on separating the contributions from a common signal and from local variations and includes a correction for the effects of diffusion and time uncertainty. We apply our approach to firn-core arrays from Dronning Maud Land (DML) in East Antarctica and from the West Antarctic Ice Sheet (WAIS). For DML and decadal to multi-centennial timescales, we find an increase in the SNR by nearly 1 order of magnitude (similar to 0.2 at decadal and similar to 1.0 at multi-centennial scales). The estimated spectrum of climate variability also shows increasing variability towards longer timescales, contrary to what is traditionally inferred from single records in this region. In contrast, the inferred variability spectrum for WAIS stays close to constant over decadal to centennial timescales, and the results even suggest a decrease in SNR over this range of timescales. We speculate that these differences between DML and WAIS are related to differences in the spatial and temporal scales of the isotope signal, highlighting the potentially more homogeneous atmospheric conditions on the Antarctic Plateau in contrast to the marine-influenced conditions on WAIS. In general, our approach provides a methodological basis for separating local proxy variability from coherent climate variations, which is applicable to a large set of palaeoclimate records.
Climate of the past : CP
10.5194/cp-14-2053-2018
1814-9324
1814-9332
wos:2018
WOS:000454054500002
Munch, T (reprint author), Helmholtz Zentrum Polar & Meeresforsch, Alfred Wegener Inst, Res Unit Potsdam, Telegrafenberg A45, D-14473 Potsdam, Germany.; Munch, T (reprint author), Univ Potsdam, Inst Phys & Astron, Karl Liebknecht Str 24-25, D-14476 Golm, Germany., thomas.muench@awi.de
Helmholtz funding through the Polar Regions and Coasts in the Changing Earth System (PACES) programme of the Alfred Wegener Institute; Initiative and Networking Fund of the Helmholtz Association [VG-NH900]; European Research Council (ERC) under the European Union's Horizon 2020
2021-07-30T07:02:27+00:00
sword
importub
filename=package.tar
e1644c64a567fb2e2a69e7bfb432680c
Münch, Thomas
false
true
CC-BY - Namensnennung 4.0 International
Thomas Münch
Thomas Laepple
Physik
Institut für Physik und Astronomie
Referiert
Import
Gold Open-Access
DOAJ gelistet
41496
2018
2018
2018
eng
xxi, 197
doctoralthesis
1
--
--
2018-06-01
Interpretation of temperature signals from ice cores
Interpretation von Temperatursignalen aus Eisbohrkernen
Earth's climate varies continuously across space and time, but humankind has witnessed only a small snapshot of its entire history, and instrumentally documented it for a mere 200 years. Our knowledge of past climate changes is therefore almost exclusively based on indirect proxy data, i.e. on indicators which are sensitive to changes in climatic variables and stored in environmental archives. Extracting the data from these archives allows retrieval of the information from earlier times. Obtaining accurate proxy information is a key means to test model predictions of the past climate, and only after such validation can the models be used to reliably forecast future changes in our warming world. The polar ice sheets of Greenland and Antarctica are one major climate archive, which record information about local air temperatures by means of the isotopic composition of the water molecules embedded in the ice. However, this temperature proxy is, as any indirect climate data, not a perfect recorder of past climatic variations. Apart from local air temperatures, a multitude of other processes affect the mean and variability of the isotopic data, which hinders their direct interpretation in terms of climate variations. This applies especially to regions with little annual accumulation of snow, such as the Antarctic Plateau. While these areas in principle allow for the extraction of isotope records reaching far back in time, a strong corruption of the temperature signal originally encoded in the isotopic data of the snow is expected. This dissertation uses observational isotope data from Antarctica, focussing especially on the East Antarctic low-accumulation area around the Kohnen Station ice-core drilling site, together with statistical and physical methods, to improve our understanding of the spatial and temporal isotope variability across different scales, and thus to enhance the applicability of the proxy for estimating past temperature variability. The presented results lead to a quantitative explanation of the local-scale (1–500 m) spatial variability in the form of a statistical noise model, and reveal the main source of the temporal variability to be the mixture of a climatic seasonal cycle in temperature and the effect of diffusional smoothing acting on temporally uncorrelated noise. These findings put significant limits on the representativity of single isotope records in terms of local air temperature, and impact the interpretation of apparent cyclicalities in the records. Furthermore, to extend the analyses to larger scales, the timescale-dependency of observed Holocene isotope variability is studied. This offers a deeper understanding of the nature of the variations, and is crucial for unravelling the embedded true temperature variability over a wide range of timescales.
Das Klima der Erde verändert sich stetig sowohl im Raum als auch in der Zeit, jedoch hat die Menschheit nur einen Bruchteil dieser Entwicklung direkt verfolgen können und erst seit 200 Jahren mit instrumentellen Beobachtungen aufgezeichnet. Unser Wissen bezüglich früherer Klimaveränderungen beruht daher fast ausschließlich auf indirekten Proxydaten, also Stellvertreterdaten, welche sensitiv auf Veränderungen in bestimmten Klimavariablen reagieren und in Klimaarchiven abgespeichert werden. Essentiell ist eine hohe Genauigkeit der erhaltenen Proxydaten. Sie erlaubt, Modellvorhersagen früherer Klimazustände quantitativ zu überprüfen und damit die Modelle zu validieren. Erst dann können mit Hilfe der Modelle verlässliche Aussagen über die anthropogen bedingten zukünftigen Klimaveränderungen getroffen werden. Die polaren Eisschilde von Grönland und Antarktika sind eines der wichtigsten Klimaarchive. Über die isotopische Zusammensetzung der im Eis eingelagerten Wassermoleküle zeichnen sie Veränderungen der lokalen Lufttemperatur auf. Jedoch stellen die Daten dieses Temperaturproxys keine perfekte Aufzeichnung früherer Klimaschwankungen dar – was im Übrigen für alle Proxydaten gilt –, da neben der Temperatur eine Fülle anderer Effekte Mittelwert und Varianz der Proxyschwankungen beeinflussen und damit die direkte Interpretation der Daten in Bezug auf klimatische Veränderungen beeinträchtigen. Insbesondere trifft dies auf Gebiete mit geringen jährlichen Schneefallmengen zu, wie z.B. das Polarplateau des antarktischen Kontinents. Diese Gebiete erlauben zwar prinzipiell die Gewinnung von Proxydatensätzen, die weit in die Vergangenheit zurückreichen, allerdings erwartet man im Allgemeinen auch eine starke Beeinträchtigung des ursprünglichen, in der isotopischen Zusammensetzung des Schnees eingeprägten Temperatursignals. Unter Verwendung von Beobachtungsdaten aus der Antarktis – hauptsächlich aus dem Niedrigakkumulationsgebiet von Dronning Maud Land in Ostantarktika, in dem auch die Kohnen-Station liegt –, sowie durch Anwendung statistischer und physikalischer Methoden, trägt diese Dissertation zu einem besseren Verständnis der räumlichen und zeitlichen Variabilität der Isotopendaten über einen weiten Skalenbereich bei. Damit verbessert die vorliegende Arbeit die Anwendbarkeit dieses Temperaturproxys in Bezug auf die Rekonstruktion natürlicher Klimavariabilität. Im Speziellen wird aus den Beobachtungsdaten ein statistisches Modell abgeleitet, welches quantitativ die lokale räumliche (1–500 m-Skala) Variabilität erklärt; des Weiteren wird gezeigt, dass die zeitliche Variabilität hauptsächlich bedingt wird durch die Kombination zweier Effekte: einen klimatischen Jahreszyklus angetrieben durch den Jahresgang der Temperatur, und die Wirkung des Diffusionsprozesses auf einen zeitlich unkorrelierten Rauschterm. Diese Resultate führen zum einen zu einer wesentlich eingegrenzten Abschätzung der Repräsentativität einzelner, isotopenbasierter Proxyzeitreihen in Bezug auf lokale Temperaturveränderungen. Zum anderen beeinflussen sie erheblich die Interpretation scheinbarer Periodizitäten im Isotopensignal. Es wird darüber hinaus vermutet, dass die Gesamtstärke des Rauschens im Isotopensignal nicht nur durch die örtliche Akkumulationsrate bestimmt wird, sondern auch durch andere Parameter wie die lokale mittlere Windstärke und die räumliche und zeitliche Kohärenz der Niederschlagswichtung. Schließlich erlaubt die Erweiterung der Analyse auf größere räumliche und zeitliche Skalen die Untersuchung, inwieweit die Variabilität isotopenbasierter Proxyzeitreihen aus dem Holozän von der Zeitskala abhängt. Dadurch wird ein tieferes Verständnis der Proxyvariabilität erzielt, welches grundlegend dafür ist, die tatsächliche, in den Daten einzelner Zeitreihen verdeckt vorhandene Temperaturvariabilität, über einen weiten Zeitskalenbereich zu entschlüsseln.
insights into the spatial and temporal variability of water isotopes in Antarctica
Einblicke in die räumliche und zeitliche Variabilität antarktischer Isotopendaten
urn:nbn:de:kobv:517-opus4-414963
online registration
Dissertation, Universität Potsdam, 2018
UT 8900
Keine öffentliche Lizenz: Unter Urheberrechtsschutz
Thomas Münch
eng
uncontrolled
climate physics
eng
uncontrolled
temperature variability
eng
uncontrolled
temperature proxy
eng
uncontrolled
proxy understanding
eng
uncontrolled
proxy uncertainty
eng
uncontrolled
stable isotopes
eng
uncontrolled
isotope variations
eng
uncontrolled
ice core
eng
uncontrolled
firn
eng
uncontrolled
noise
eng
uncontrolled
post-depositional
eng
uncontrolled
two-dimensional
eng
uncontrolled
Antarctica
eng
uncontrolled
Dronning Maud Land
eng
uncontrolled
Kohnen
deu
uncontrolled
Klimaphysik
deu
uncontrolled
Klimavariabilität
deu
uncontrolled
Temperaturproxy
deu
uncontrolled
Proxyverständnis
deu
uncontrolled
Proxyunsicherheit
deu
uncontrolled
stabile Isotope
deu
uncontrolled
Eisbohrkern
deu
uncontrolled
Antarktis
deu
uncontrolled
Dronning Maud Land
deu
uncontrolled
Kohnen
Physik
Hydrospheric and atmospheric geophysics
open_access
Institut für Physik und Astronomie
Extern
Universität Potsdam
Universität Potsdam
https://publishup.uni-potsdam.de/files/41496/muench_diss.pdf