On the similarity and apparent cycles of isotopic variations in East Antarctic snow pits
Stable isotope ratios δ 18 O and δ 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 o...
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Online Access: | https://doi.org/10.5194/tc-12-169-2018 https://tc.copernicus.org/articles/12/169/2018/ |
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ftcopernicus:oai:publications.copernicus.org:tc61532 2023-05-15T13:54:27+02:00 On the similarity and apparent cycles of isotopic variations in East Antarctic snow pits Laepple, Thomas Münch, Thomas Casado, Mathieu Hoerhold, Maria Landais, Amaelle Kipfstuhl, Sepp 2018-09-27 info:eu-repo/semantics/application/pdf https://doi.org/10.5194/tc-12-169-2018 https://tc.copernicus.org/articles/12/169/2018/ eng eng info:eu-repo/grantAgreement/EC/FP7/306045 doi:10.5194/tc-12-169-2018 https://tc.copernicus.org/articles/12/169/2018/ info:eu-repo/semantics/openAccess eISSN: 1994-0424 info:eu-repo/semantics/Text 2018 ftcopernicus https://doi.org/10.5194/tc-12-169-2018 2020-07-20T16:23:27Z Stable isotope ratios δ 18 O and δ 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 δ 18 O and δ 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 δ 18 O and δ D profiles with typical wavelengths of ∼ 20 cm. These observations are unexpected as the accumulation rates strongly differ between the sites, ranging from 20 to 80 mm w. e. yr −1 ( ∼ 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 δ 18 O and δ D variations in high-resolution firn profiles from eight East Antarctic sites. First, we confirm the suggested cycle length (mean distance between peaks) of ∼ 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 apparent 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. Other/Unknown Material Antarc* Antarctic Antarctica East Antarctica Copernicus Publications: E-Journals Antarctic East Antarctica The Antarctic The Cryosphere 12 1 169 187 |
institution |
Open Polar |
collection |
Copernicus Publications: E-Journals |
op_collection_id |
ftcopernicus |
language |
English |
description |
Stable isotope ratios δ 18 O and δ 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 δ 18 O and δ 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 δ 18 O and δ D profiles with typical wavelengths of ∼ 20 cm. These observations are unexpected as the accumulation rates strongly differ between the sites, ranging from 20 to 80 mm w. e. yr −1 ( ∼ 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 δ 18 O and δ D variations in high-resolution firn profiles from eight East Antarctic sites. First, we confirm the suggested cycle length (mean distance between peaks) of ∼ 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 apparent 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. |
format |
Other/Unknown Material |
author |
Laepple, Thomas Münch, Thomas Casado, Mathieu Hoerhold, Maria Landais, Amaelle Kipfstuhl, Sepp |
spellingShingle |
Laepple, Thomas Münch, Thomas Casado, Mathieu Hoerhold, Maria Landais, Amaelle Kipfstuhl, Sepp On the similarity and apparent cycles of isotopic variations in East Antarctic snow pits |
author_facet |
Laepple, Thomas Münch, Thomas Casado, Mathieu Hoerhold, Maria Landais, Amaelle Kipfstuhl, Sepp |
author_sort |
Laepple, Thomas |
title |
On the similarity and apparent cycles of isotopic variations in East Antarctic snow pits |
title_short |
On the similarity and apparent cycles of isotopic variations in East Antarctic snow pits |
title_full |
On the similarity and apparent cycles of isotopic variations in East Antarctic snow pits |
title_fullStr |
On the similarity and apparent cycles of isotopic variations in East Antarctic snow pits |
title_full_unstemmed |
On the similarity and apparent cycles of isotopic variations in East Antarctic snow pits |
title_sort |
on the similarity and apparent cycles of isotopic variations in east antarctic snow pits |
publishDate |
2018 |
url |
https://doi.org/10.5194/tc-12-169-2018 https://tc.copernicus.org/articles/12/169/2018/ |
geographic |
Antarctic East Antarctica The Antarctic |
geographic_facet |
Antarctic East Antarctica The Antarctic |
genre |
Antarc* Antarctic Antarctica East Antarctica |
genre_facet |
Antarc* Antarctic Antarctica East Antarctica |
op_source |
eISSN: 1994-0424 |
op_relation |
info:eu-repo/grantAgreement/EC/FP7/306045 doi:10.5194/tc-12-169-2018 https://tc.copernicus.org/articles/12/169/2018/ |
op_rights |
info:eu-repo/semantics/openAccess |
op_doi |
https://doi.org/10.5194/tc-12-169-2018 |
container_title |
The Cryosphere |
container_volume |
12 |
container_issue |
1 |
container_start_page |
169 |
op_container_end_page |
187 |
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1766260311718887424 |