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<sub>3</sub><sup>−</sup>) in snow. Seven snowpits from sites with accumulation rates between 24...
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2015-08-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/15/9435/2015/acp-15-9435-2015.pdf |
| _version_ | 1819263147516624896 |
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| author | G. Shi A. M. Buffen M. G. Hastings C. Li H. Ma Y. Li B. Sun C. An S. Jiang |
| author_facet | G. Shi A. M. Buffen M. G. Hastings C. Li H. Ma Y. Li B. Sun C. An S. Jiang |
| author_sort | G. Shi |
| collection | DOAJ |
| 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<sub>3</sub><sup>−</sup>) in snow. Seven snowpits from sites with accumulation
rates between 24 and 172 kg m<sup>−2</sup> a<sup>−1</sup> were sampled to depths of
150 to 300 cm. At sites from the continental interior (low accumulation,
< 55 kg m<sup>−2</sup> a<sup>−1</sup>), nitrate mass fraction is generally
> 200 ng g<sup>−1</sup> in surface snow and decreases quickly with
depth to < 50 ng g<sup>−1</sup>. Considerably increasing values of
δ<sup>15</sup>N of nitrate are also observed (16–461 ‰
vs. air N<sub>2</sub>), particularly in the top 20 cm, which is consistent with
predicted fractionation constants for the photolysis of nitrate. The
δ<sup>18</sup>O of nitrate (17–84 ‰ vs. VSMOW (Vienna Standard Mean Ocean
Water)), on the
other hand, decreases with increasing δ<sup>15</sup>N, suggestive of
secondary formation of nitrate in situ (following photolysis) with a low
δ<sup>18</sup>O source. Previous studies have suggested that δ<sup>15</sup>N and δ<sup>18</sup>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<sup>18</sup>O changes, with increasing
δ<sup>18</sup>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<sup>−2</sup> a<sup>−1</sup>), 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<sup>15</sup>N (−15–71 ‰ vs. air N<sub>2</sub>) and higher in δ<sup>18</sup>O of
nitrate (53–111 ‰ vs. VSMOW). The relationships found
amongst mass fraction, δ<sup>15</sup>N, δ<sup>18</sup>O and Δ<sup>17</sup>O (Δ<sup>17</sup>O = δ<sup>17</sup>O–0.52 × δ<sup>18</sup>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. |
| first_indexed | 2024-12-23T20:08:58Z |
| format | Article |
| id | doaj.art-fa026c7d6d3e47b986fcc55d6fdaa9e6 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-12-23T20:08:58Z |
| publishDate | 2015-08-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-fa026c7d6d3e47b986fcc55d6fdaa9e62022-12-21T17:32:51ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242015-08-0115169435945310.5194/acp-15-9435-2015Investigation of post-depositional processing of nitrate in East Antarctic snow: isotopic constraints on photolytic loss, re-oxidation, and source inputsG. Shi0A. M. Buffen1M. G. Hastings2C. Li3H. Ma4Y. Li5B. Sun6C. An7S. Jiang8Key Laboratory for Polar Science of State Oceanic Administration, Polar Research Institute of China, Shanghai 200062, ChinaDepartment of Earth, Environmental and Planetary Sciences and Institute at Brown for Environment and Society, Brown University, Providence, Rhode Island 02912, USADepartment of Earth, Environmental and Planetary Sciences and Institute at Brown for Environment and Society, Brown University, Providence, Rhode Island 02912, USAThe State Key Laboratory of the Cryospheric Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, ChinaKey Laboratory for Polar Science of State Oceanic Administration, Polar Research Institute of China, Shanghai 200062, ChinaKey Laboratory for Polar Science of State Oceanic Administration, Polar Research Institute of China, Shanghai 200062, ChinaKey Laboratory for Polar Science of State Oceanic Administration, Polar Research Institute of China, Shanghai 200062, ChinaKey Laboratory for Polar Science of State Oceanic Administration, Polar Research Institute of China, Shanghai 200062, ChinaKey Laboratory for Polar Science of State Oceanic Administration, Polar Research Institute of China, Shanghai 200062, ChinaSnowpits 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<sub>3</sub><sup>−</sup>) in snow. Seven snowpits from sites with accumulation rates between 24 and 172 kg m<sup>−2</sup> a<sup>−1</sup> were sampled to depths of 150 to 300 cm. At sites from the continental interior (low accumulation, < 55 kg m<sup>−2</sup> a<sup>−1</sup>), nitrate mass fraction is generally > 200 ng g<sup>−1</sup> in surface snow and decreases quickly with depth to < 50 ng g<sup>−1</sup>. Considerably increasing values of δ<sup>15</sup>N of nitrate are also observed (16–461 ‰ vs. air N<sub>2</sub>), particularly in the top 20 cm, which is consistent with predicted fractionation constants for the photolysis of nitrate. The δ<sup>18</sup>O of nitrate (17–84 ‰ vs. VSMOW (Vienna Standard Mean Ocean Water)), on the other hand, decreases with increasing δ<sup>15</sup>N, suggestive of secondary formation of nitrate in situ (following photolysis) with a low δ<sup>18</sup>O source. Previous studies have suggested that δ<sup>15</sup>N and δ<sup>18</sup>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<sup>18</sup>O changes, with increasing δ<sup>18</sup>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<sup>−2</sup> a<sup>−1</sup>), 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<sup>15</sup>N (−15–71 ‰ vs. air N<sub>2</sub>) and higher in δ<sup>18</sup>O of nitrate (53–111 ‰ vs. VSMOW). The relationships found amongst mass fraction, δ<sup>15</sup>N, δ<sup>18</sup>O and Δ<sup>17</sup>O (Δ<sup>17</sup>O = δ<sup>17</sup>O–0.52 × δ<sup>18</sup>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.http://www.atmos-chem-phys.net/15/9435/2015/acp-15-9435-2015.pdf |
| spellingShingle | G. Shi A. M. Buffen M. G. Hastings C. Li H. Ma Y. Li B. Sun C. An S. Jiang Investigation of post-depositional processing of nitrate in East Antarctic snow: isotopic constraints on photolytic loss, re-oxidation, and source inputs Atmospheric Chemistry and Physics |
| title | 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_short | 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 |
| url | http://www.atmos-chem-phys.net/15/9435/2015/acp-15-9435-2015.pdf |
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