Investigation of post-depositional processing of nitrate in East Antarctic snow: isotopic constraints on photolytic loss, re-oxidation, and source inputs

Snowpits along a traverse from coastal East Antarctica to the summit of the ice sheet (Dome Argus) are used to investigate the post-depositional processing of nitrate (NO 3 − ) in snow. Seven snowpits from sites with accumulation rates between 24 and 172 kg m −2 a −1 were sampled to depths of 150 to...

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Published in:Atmospheric Chemistry and Physics
Main Authors: Shi, G., Buffen, A. M., Hastings, M. G., Li, C., Ma, H., Li, Y., Sun, B., An, C., Jiang, S.
Format: Text
Language:English
Published: 2018
Subjects:
Online Access:https://doi.org/10.5194/acp-15-9435-2015
https://www.atmos-chem-phys.net/15/9435/2015/
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spelling ftcopernicus:oai:publications.copernicus.org:acp27553 2023-05-15T13:43:09+02:00 Investigation of post-depositional processing of nitrate in East Antarctic snow: isotopic constraints on photolytic loss, re-oxidation, and source inputs Shi, G. Buffen, A. M. Hastings, M. G. Li, C. Ma, H. Li, Y. Sun, B. An, C. Jiang, S. 2018-09-13 application/pdf https://doi.org/10.5194/acp-15-9435-2015 https://www.atmos-chem-phys.net/15/9435/2015/ eng eng doi:10.5194/acp-15-9435-2015 https://www.atmos-chem-phys.net/15/9435/2015/ eISSN: 1680-7324 Text 2018 ftcopernicus https://doi.org/10.5194/acp-15-9435-2015 2019-12-24T09:53:10Z Snowpits along a traverse from coastal East Antarctica to the summit of the ice sheet (Dome Argus) are used to investigate the post-depositional processing of nitrate (NO 3 − ) in snow. Seven snowpits from sites with accumulation rates between 24 and 172 kg m −2 a −1 were sampled to depths of 150 to 300 cm. At sites from the continental interior (low accumulation, < 55 kg m −2 a −1 ), nitrate mass fraction is generally > 200 ng g −1 in surface snow and decreases quickly with depth to < 50 ng g −1 . Considerably increasing values of δ 15 N of nitrate are also observed (16–461 ‰ vs. air N 2 ), particularly in the top 20 cm, which is consistent with predicted fractionation constants for the photolysis of nitrate. The δ 18 O of nitrate (17–84 ‰ vs. VSMOW (Vienna Standard Mean Ocean Water)), on the other hand, decreases with increasing δ 15 N, suggestive of secondary formation of nitrate in situ (following photolysis) with a low δ 18 O source. Previous studies have suggested that δ 15 N and δ 18 O of nitrate at deeper snow depths should be predictable based upon an exponential change derived near the surface. At deeper depths sampled in this study, however, the relationship between nitrate mass fraction and δ 18 O changes, with increasing δ 18 O of nitrate observed between 100 and 200 cm. Predicting the impact of post-depositional loss, and therefore changes in the isotopes with depth, is highly sensitive to the depth interval over which an exponential change is assumed. In the snowpits collected closer to the coast (accumulation > 91 kg m −2 a −1 ), there are no obvious trends detected with depth and instead seasonality in nitrate mass fraction and isotopic composition is found. In comparison to the interior sites, the coastal pits are lower in δ 15 N (−15–71 ‰ vs. air N 2 ) and higher in δ 18 O of nitrate (53–111 ‰ vs. VSMOW). The relationships found amongst mass fraction, δ 15 N, δ 18 O and Δ 17 O (Δ 17 O = δ 17 O–0.52 × δ 18 O) of nitrate cannot be explained by local post-depositional processes alone, and are instead interpreted in the context of a primary atmospheric signal. Consistent with other Antarctic observational and modeling studies, the isotopic results are suggestive of an important influence of stratospheric ozone chemistry on nitrate formation during the cold season and a mix of tropospheric sources and chemistry during the warm season. Overall, the findings in this study speak to the sensitivity of nitrate isotopic composition to post-depositional processing and highlight the strength of combined use of the nitrogen and oxygen isotopes for a mechanistic understanding of this processing. Text Antarc* Antarctic Antarctica East Antarctica Ice Sheet Copernicus Publications: E-Journals Antarctic Dome Argus ENVELOPE(77.000,77.000,-81.000,-81.000) East Antarctica Atmospheric Chemistry and Physics 15 16 9435 9453
institution Open Polar
collection Copernicus Publications: E-Journals
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language English
description Snowpits along a traverse from coastal East Antarctica to the summit of the ice sheet (Dome Argus) are used to investigate the post-depositional processing of nitrate (NO 3 − ) in snow. Seven snowpits from sites with accumulation rates between 24 and 172 kg m −2 a −1 were sampled to depths of 150 to 300 cm. At sites from the continental interior (low accumulation, < 55 kg m −2 a −1 ), nitrate mass fraction is generally > 200 ng g −1 in surface snow and decreases quickly with depth to < 50 ng g −1 . Considerably increasing values of δ 15 N of nitrate are also observed (16–461 ‰ vs. air N 2 ), particularly in the top 20 cm, which is consistent with predicted fractionation constants for the photolysis of nitrate. The δ 18 O of nitrate (17–84 ‰ vs. VSMOW (Vienna Standard Mean Ocean Water)), on the other hand, decreases with increasing δ 15 N, suggestive of secondary formation of nitrate in situ (following photolysis) with a low δ 18 O source. Previous studies have suggested that δ 15 N and δ 18 O of nitrate at deeper snow depths should be predictable based upon an exponential change derived near the surface. At deeper depths sampled in this study, however, the relationship between nitrate mass fraction and δ 18 O changes, with increasing δ 18 O of nitrate observed between 100 and 200 cm. Predicting the impact of post-depositional loss, and therefore changes in the isotopes with depth, is highly sensitive to the depth interval over which an exponential change is assumed. In the snowpits collected closer to the coast (accumulation > 91 kg m −2 a −1 ), there are no obvious trends detected with depth and instead seasonality in nitrate mass fraction and isotopic composition is found. In comparison to the interior sites, the coastal pits are lower in δ 15 N (−15–71 ‰ vs. air N 2 ) and higher in δ 18 O of nitrate (53–111 ‰ vs. VSMOW). The relationships found amongst mass fraction, δ 15 N, δ 18 O and Δ 17 O (Δ 17 O = δ 17 O–0.52 × δ 18 O) of nitrate cannot be explained by local post-depositional processes alone, and are instead interpreted in the context of a primary atmospheric signal. Consistent with other Antarctic observational and modeling studies, the isotopic results are suggestive of an important influence of stratospheric ozone chemistry on nitrate formation during the cold season and a mix of tropospheric sources and chemistry during the warm season. Overall, the findings in this study speak to the sensitivity of nitrate isotopic composition to post-depositional processing and highlight the strength of combined use of the nitrogen and oxygen isotopes for a mechanistic understanding of this processing.
format Text
author Shi, G.
Buffen, A. M.
Hastings, M. G.
Li, C.
Ma, H.
Li, Y.
Sun, B.
An, C.
Jiang, S.
spellingShingle Shi, G.
Buffen, A. M.
Hastings, M. G.
Li, C.
Ma, H.
Li, Y.
Sun, B.
An, C.
Jiang, S.
Investigation of post-depositional processing of nitrate in East Antarctic snow: isotopic constraints on photolytic loss, re-oxidation, and source inputs
author_facet Shi, G.
Buffen, A. M.
Hastings, M. G.
Li, C.
Ma, H.
Li, Y.
Sun, B.
An, C.
Jiang, S.
author_sort Shi, G.
title Investigation of post-depositional processing of nitrate in East Antarctic snow: isotopic constraints on photolytic loss, re-oxidation, and source inputs
title_short Investigation of post-depositional processing of nitrate in East Antarctic snow: isotopic constraints on photolytic loss, re-oxidation, and source inputs
title_full Investigation of post-depositional processing of nitrate in East Antarctic snow: isotopic constraints on photolytic loss, re-oxidation, and source inputs
title_fullStr Investigation of post-depositional processing of nitrate in East Antarctic snow: isotopic constraints on photolytic loss, re-oxidation, and source inputs
title_full_unstemmed Investigation of post-depositional processing of nitrate in East Antarctic snow: isotopic constraints on photolytic loss, re-oxidation, and source inputs
title_sort investigation of post-depositional processing of nitrate in east antarctic snow: isotopic constraints on photolytic loss, re-oxidation, and source inputs
publishDate 2018
url https://doi.org/10.5194/acp-15-9435-2015
https://www.atmos-chem-phys.net/15/9435/2015/
long_lat ENVELOPE(77.000,77.000,-81.000,-81.000)
geographic Antarctic
Dome Argus
East Antarctica
geographic_facet Antarctic
Dome Argus
East Antarctica
genre Antarc*
Antarctic
Antarctica
East Antarctica
Ice Sheet
genre_facet Antarc*
Antarctic
Antarctica
East Antarctica
Ice Sheet
op_source eISSN: 1680-7324
op_relation doi:10.5194/acp-15-9435-2015
https://www.atmos-chem-phys.net/15/9435/2015/
op_doi https://doi.org/10.5194/acp-15-9435-2015
container_title Atmospheric Chemistry and Physics
container_volume 15
container_issue 16
container_start_page 9435
op_container_end_page 9453
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