Snow accumulation rate and atmospheric oxidation pathway proxies from nitrate isotopes in East Antarctica

2020 ◽  
Author(s):  
Pete Akers ◽  
Joël Savarino ◽  
Nicolas Caillon
Keyword(s):  
Oxygen Isotope ◽  
Accumulation Rate ◽  
Isotopic Fractionation ◽  
Ice Cores ◽  
Snow Accumulation ◽  
East Antarctica ◽  
Atmospheric Oxidation ◽  
High Accumulation ◽  
Antarctic Snow ◽  
History Of

<p>Nitrate is naturally deposited in Antarctic snow and is detectable at low concentrations throughout our deepest ice cores. However, nitrate is photoreactive under ultraviolet light and experiences significant post-depositional loss. This nitrate loss favors 14NO3- over 15NO3-, and the resulting isotopic fractionation can be used as a proxy for duration of sunlight exposure. Here, we present nitrate isotope data (δ15N, δ18O, Δ17O) sampled from shallow snow cores and pits across East Antarctica. Our >30 sampling sites extend from coastal Adélie Land onto the high East Antarctic Plateau at Dome C and beyond, covering annual snow mass balances that range from 240 mm/yr to less than 30 mm/yr (water equivalent). The δ15N of nitrate at these sites show an inverse relationship with snow accumulation rate, with δ15N ≈ 20‰ at the coastal sites with the highest accumulations and δ15N ≈ 150-250‰ at the driest inland sites. This relationship develops because newly deposited nitrate is buried below the level of light penetration by new snow relatively quickly at high accumulation sites, but nitrate at drier sites can be exposed to sunlight for several years. After burial below the reach of sunlight, the δ15N signature of nitrate is preserved and thus offers a new proxy for snow accumulation rate in East Antarctic ice cores. In contrast, the oxygen isotopes of nitrate isotopically exchange with surrounding ice after burial, which complicates their interpretation. However, our large sample set allows an estimation of the rate of isotopic exchange at various sites, and the original isotopic values at the time of deposition may be approximated after correcting for this rate of exchange. These oxygen isotope values likely reflect in part the atmospheric oxidation history of the nitrate and its nitrogen oxide progenitor, but further study is needed to fully understand nitrate oxygen isotope dynamics.</p>

Reconstructing Antarctic snow accumulation using nitrogen isotopes of nitrate

2021 ◽  
Author(s):  
Pete D. Akers ◽  
Joël Savarino ◽  
Nicolas Caillon ◽  
Mark Curran ◽  
Tas Van Ommen
Keyword(s):  
Nitrogen Isotopes ◽  
Full Range ◽  
Ice Core ◽  
Ice Cores ◽  
Snow Accumulation ◽  
East Antarctica ◽  
Accumulation Rates ◽  
Sea Levels ◽  
Antarctic Snow ◽  
Parallel Reconstruction

<p>Precise Antarctic snow accumulation estimates are needed to understand past and future changes in global sea levels, but standard reconstructions using water isotopes suffer from competing isotopic effects external to accumulation. We present here an alternative accumulation proxy based on the post-depositional photolytic fractionation of nitrogen isotopes (d<sup>15</sup>N) in nitrate. On the high plateau of East Antarctica, sunlight penetrating the uppermost snow layers converts snow-borne nitrate into nitrogen oxide gas that can be lost to the atmosphere. This nitrate loss favors <sup>14</sup>NO<sub>3</sub><sup>-</sup> over <sup>15</sup>NO<sub>3</sub><sup>-</sup>, and thus the d<sup>15</sup>N of nitrate remaining in the snow will steadily increase until the nitrate is eventually buried beneath the reach of light. Because the duration of time until burial is dependent upon the rate of net snow accumulation, sites with lower accumulation rates have a longer burial wait and thus higher d<sup>15</sup>N values. A linear relationship (r<sup>2</sup> = 0.86) between d<sup>15</sup>N and net accumulation<sup>-1</sup> is calculated from over 120 samples representing 105 sites spanning East Antarctica. These sites largely encompass the full range of snow accumulation rates observed in East Antarctica, from 25 kg m-<sup>2</sup> yr<sup>-1</sup> at deep interior sites to >400 kg m-<sup>2</sup> yr<sup>-1</sup> at near coastal sites. We apply this relationship as a transfer function to an Aurora Basin ice core to produce a 700-year record of accumulation changes. Our nitrate-based estimate compares very well with a parallel reconstruction for Aurora Basin that uses volcanic horizons and ice-penetrating radar. Continued improvements to our database may enable precise independent estimates of millennial-scale accumulation changes using deep ice cores such as EPICA Dome C and Beyond EPICA-Oldest Ice.</p>

scholarly journals Enhanced Moisture Delivery into Victoria Land, East Antarctica During the Early Last Interglacial: Implications for West Antarctic Ice Sheet Stability

2021 ◽  
Author(s):  
Yuzhen Yan ◽  
Nicole E. Spaulding ◽  
Michael L. Bender ◽  
Edward J. Brook ◽  
John A. Higgins ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Ice Cores ◽  
Snow Accumulation ◽  
East Antarctica ◽  
Ice Age ◽  
Accumulation Rates ◽  
Last Interglacial ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Victoria Land

Abstract. The S27 ice core, drilled in the Allan Hills Blue Ice Area of East Antarctica, is located in Southern Victoria Land ~80 km away from the present-day northern edge of the Ross Ice Shelf. Here, we utilize the reconstructed accumulation rate of S27 covering the Last Interglacial (LIG) period between 129 and 116 thousand years before present (ka) to infer moisture transport into the region. The accumulation rate is based on the ice age-gas age differences calculated from the ice chronology, which is constrained by the stable water isotopes of the ice, and an improved gas chronology based on measurements of oxygen isotopes of O2 in the trapped gases. The peak accumulation rate in S27 occurred at 128.2 ka, near the peak LIG warming in Antarctica. Even the most conservative estimate yields a six-fold increase in the accumulation rate in the LIG, whereas other Antarctic ice cores are typically characterized by a glacial-interglacial difference of a factor of two to three. While part of the increase in S27 accumulation rates must originate from changes in the large-scale atmospheric circulation, additional mechanisms are needed to explain the large changes. We hypothesize that the exceptionally high snow accumulation recorded in S27 reflects open-ocean conditions in the Ross Sea, created by reduced sea ice extent and increased polynya size, and perhaps by a southward retreat of the Ross Ice Shelf relative to its present-day position near the onset of LIG. The proposed ice shelf retreat would also be compatible with a sea-level high stand around 129 ka significantly sourced from West Antarctica. The peak in S27 accumulation rates is transient, suggesting that if the Ross Ice Shelf had indeed retreated during the early LIG, it would have re-advanced by 125 ka.

scholarly journals Modelling firn thickness evolution during the last deglaciation: constraints on sensitivity to temperature and impurities

2017 ◽  
Vol 13 (7) ◽  
pp. 833-853 ◽  
Author(s):  
Camille Bréant ◽  
Patricia Martinerie ◽  
Anaïs Orsi ◽  
Laurent Arnaud ◽  
Amaëlle Landais
Keyword(s):  
Accumulation Rate ◽  
Ice Cores ◽  
East Antarctica ◽  
Ice Age ◽  
Age Difference ◽  
Last Deglaciation ◽  
Densification Rate ◽  
Impurity Effects ◽  
High Accumulation ◽  
The Last Deglaciation

Abstract. The transformation of snow into ice is a complex phenomenon that is difficult to model. Depending on surface temperature and accumulation rate, it may take several decades to millennia for air to be entrapped in ice. The air is thus always younger than the surrounding ice. The resulting gas–ice age difference is essential to documenting the phasing between CO2 and temperature changes, especially during deglaciations. The air trapping depth can be inferred in the past using a firn densification model, or using δ15N of air measured in ice cores. All firn densification models applied to deglaciations show a large disagreement with δ15N measurements at several sites in East Antarctica, predicting larger firn thickness during the Last Glacial Maximum, whereas δ15N suggests a reduced firn thickness compared to the Holocene. Here we present modifications of the LGGE firn densification model, which significantly reduce the model–data mismatch for the gas trapping depth evolution over the last deglaciation at the coldest sites in East Antarctica (Vostok, Dome C), while preserving the good agreement between measured and modelled modern firn density profiles. In particular, we introduce a dependency of the creep factor on temperature and impurities in the firn densification rate calculation. The temperature influence intends to reflect the dominance of different mechanisms for firn compaction at different temperatures. We show that both the new temperature parameterization and the influence of impurities contribute to the increased agreement between modelled and measured δ15N evolution during the last deglaciation at sites with low temperature and low accumulation rate, such as Dome C or Vostok. We find that a very low sensitivity of the densification rate to temperature has to be used in the coldest conditions. The inclusion of impurity effects improves the agreement between modelled and measured δ15N at cold East Antarctic sites during the last deglaciation, but deteriorates the agreement between modelled and measured δ15N evolution at Greenland and Antarctic sites with high accumulation unless threshold effects are taken into account. We thus do not provide a definite solution to the firnification at very cold Antarctic sites but propose potential pathways for future studies.

scholarly journals Spatial variability at shallow snow-layer depths in central Dronning Maud Land, East Antarctica

1999 ◽  
Vol 29 ◽  
pp. 10-16 ◽  
Author(s):  
Cecilia Richardson ◽  
Per Holmlund
Keyword(s):  
Spatial Variability ◽  
Accumulation Rate ◽  
Marked Change ◽  
Ice Cores ◽  
Snow Accumulation ◽  
East Antarctica ◽  
Snow Layer ◽  
Accumulation Pattern ◽  
Single Action ◽  
Dronning Maud Land

AbstractThe spatial variability in snow accumulation varies between different regions in Dronning Maud Land, East Antarctica. This pattern cannot easily be explained by the single action of parameters such as distance to open sea, surface elevation or slope. In 1996-97 we mapped snow-layer depths within the top 11 m of the snowpack with a ground-based radar along a 500 km traverse on the polar plateau in central Dronning Maud Land. The results showed that the general accumulation pattern could be described by three major characteristic sections: a pronounced trend of decreasing net accumulation with increasing altitude from 2400 to 2840 m a.s.l.; relatively high erosion rates and occurrence of areas with net erosion at 2840-3140 m a.s.l.; and a slight trend of decreasing net accumulation with increasing altitude from 3140 to 3450 m a.s.l. The spatial variability in snow-layer depths showed a marked change around 3080 m a.s.l., with high variability at lower elevations and low variability at higher elevations. We also determined the spatial representativeness of 11 firn cores drilled along the traverse. In general, the representativeness of the cores was high. However, the core with the lowest representativeness underestimated the mean accumulation rate around the coring site by 22%. This shows that snow-radar data on spatial snow distribution are important for the interpretation of accumulation rates obtained from firn and ice cores.

scholarly journals Distribution of oxygen isotope ratios and snow accumulation rates in Wilhelm II Land, East Antarctica

2002 ◽  
Vol 35 ◽  
pp. 107-110 ◽  
Author(s):  
Barbara T. Smith ◽  
Tas D. van Ommen ◽  
Vin I. Morgan
Keyword(s):  
Oxygen Isotope ◽  
Accumulation Rate ◽  
Isotope Ratios ◽  
Snow Accumulation ◽  
East Antarctica ◽  
Simple Relationship ◽  
Accumulation Rates ◽  
Ice Shelf ◽  
The West ◽  
Oxygen Isotope Ratios

AbstractRecords of recent oxygen isotope ratios (δ18O) and accumulation rates are presented for the region of Wilhelm II Land, East Antarctica, between 78˚ and 93˚E and from the coast to 2100m elevation. These records were derived from analysis of 21 shallow firn cores collected during the 1997/98 and 1998/99 Australian National Antarctic Research Expeditions summer operations. the accumulation rates were determined using comparisons between detailed analyses of density, δ18O, hydrogen peroxide (H2O2) levels and electrical conductivity. the δ18O distribution follows an approximately linear relationship with snow surface elevation, with values from –22‰ near the coast to –32‰ towards 2000m elevation. Accumulation-rate distribution does not display this simple relationship with topography. South of the West Ice Shelf the contours run parallel to lines of latitude (oblique to the coast and topography), with 400 kg m–2 a–1 towards the coast and 2000m elevation, and a lower zone of 300 kg m–2 a–1 along an axis of 68.4˚ S. This pattern of accumulation is also evident along the Mirny–Vostok traverse route. Southwest of the West Ice Shelf the rate of accumulation drops gradually from 300 to 200 kg m–2 a–1 towards Lambert Glacier basin. Surface-snow redistribution and variations in accumulation rate cause variability in the clarity of core records, but several sites show sufficient stratigraphic preservation to suggest potential for extraction of extended palaeoenvironmental records through further drilling.

scholarly journals High resolution 900 yr volcanic and climatic record from the Vostok area, East Antarctica

2013 ◽  
Vol 7 (3) ◽  
pp. 1961-1986 ◽  
Author(s):  
E. Yu. Osipov ◽  
T. V. Khodzher ◽  
L. P. Golobokova ◽  
N. A. Onischuk ◽  
V. Ya. Lipenkov ◽  
...  
Keyword(s):  
High Resolution ◽  
Environmental Changes ◽  
Atmospheric Transport ◽  
Accumulation Rate ◽  
Ice Cores ◽  
High Sensitivity ◽  
Snow Accumulation ◽  
East Antarctica ◽  
Positive Trend ◽  
Decadal Scale

Abstract. Detailed volcanic record of the last 900 yr (1093–2010 AD) has been received using high resolution (2–3 samples per accumulation year) sulfate measurements in four snow/firn cores from the Vostok station area, East Antarctica. Totally, 33 volcanic events have been identified in the record, including well-known low latitude eruption signals found in many polar ice cores (e.g., Pinatubo 1991, Agung 1963, Krakatoa 1883, Tambora 1815, Huanaputina 1600, Kuwae 1452), however in comparison with other Antarctic sites the record has more events covering the last 900 yr. The strongest volcanic signals occurred during mid-13th, mid-15th and 18th centuries. The largest volcanic signal of Vostok (both in sulfate concentration and flux) is the 1452 AD Kuwae eruption. Average snow accumulation rate calculated for the period 1093–2010 AD is 21.3 ± 2.3 mm H2O. Accumulation record demonstrates a slight positive trend, however sharply increased accumulation rate during the periods from 1600 to 1815 AD (by 11% from long-term mean) and from 1963 to 2010 AD (by 15%) are typical features of the site. Na+ record shows strong decadal-scale variability probably connected with coupled changes in atmospheric transport patterns over Antarctica (meridional circulation change) and local glaciology. The obtained high resolution climatic records suggest a high sensitivity of the Vostok location to environmental changes in Southern Hemisphere.

scholarly journals Post-depositional movement of methanesulphonic acid at Law Dome, Antarctica, and the influence of accumulation rate

2002 ◽  
Vol 35 ◽  
pp. 333-339 ◽  
Author(s):  
Mark A.J. Curran ◽  
Anne S. Palmer ◽  
Tas D. van Ommen ◽  
Vin I. Morgan ◽  
Katrina L. Phillips ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Ice Cores ◽  
Snow Accumulation ◽  
Sea Salt ◽  
Accumulation Rates ◽  
Surface Layers ◽  
Sea Salts ◽  
High Accumulation ◽  
Air Masses ◽  
Salt Ions

AbstractA series of ice cores from sites with different snow-accumulation rates across Law Dome, East Antarctica, was investigated for methanesulphonic acid (MSA) movement. the precipitation at these sites (up to 35 km apart) is influenced by the same air masses, the principal difference being the accumulation rate. At the low-accumulation-rate W20k site (0.17m ice equivalent), MSAwas completely relocated from the summer to winter layer. Moderate movement was observed at the intermediate-accumulation-rate site (0.7m ice equivalent), Dome Summit South (DSS), while there was no evidence of movement at the high-accumulation-rate DE08 site (1.4m ice equivalent). the main DSS record of MSA covered the epoch AD 1727–2000 and was used to investigate temporal post-depositional changes. Co-deposition of MSA and sea-salt ions was observed in the surface layers, outside of the main summer MSA peak,which complicates interpretation of these peaks as evidence of movement in deeper layers. A seasonal study of the 273 year DSS record revealed MSA migration predominantly from summer into autumn (in the up-core direction), but this migration was suppressed during the Tambora (1815) and unknown (1809) volcanic eruption period, and enhanced during an epoch (1770–1800) with high summer nitrate levels. A complex interaction between the gradients in nss-sulphate, nitrate and sea salts (which are influenced by accumulation rate) is believed to control the rate and extent of movement of MSA.

scholarly journals High-resolution 900 year volcanic and climatic record from the Vostok area, East Antarctica

2014 ◽  
Vol 8 (3) ◽  
pp. 843-851 ◽  
Author(s):  
E. Y. Osipov ◽  
T. V. Khodzher ◽  
L. P. Golobokova ◽  
N. A. Onischuk ◽  
V. Y. Lipenkov ◽  
...  
Keyword(s):  
Atmospheric Transport ◽  
Accumulation Rate ◽  
Ice Cores ◽  
Snow Accumulation ◽  
East Antarctica ◽  
Low Latitude ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns ◽  
Vostok Station ◽  
Climatic Record

Abstract. Ion chromatography measurements of 1730 snow and firn samples obtained from three short cores and one pit in the Vostok station area, East Antarctica, allowed for the production of the combined volcanic record of the last 900 years (AD 1093–2010). The resolution of the record is 2–3 samples per accumulation year. In total, 24 volcanic events have been identified, including seven well-known low-latitude eruptions (Pinatubo 1991, Agung 1963, Krakatoa 1883, Tambora 1815, Huanaputina 1600, Kuwae 1452, El Chichon 1259) found in most of the polar ice cores. In comparison with three other East Antarctic volcanic records (South Pole, Plateau Remote and Dome C), the Vostok record contains more events within the last 900 years. The differences between the records may be explained by local glaciological conditions, volcanic detection methodology, and, probably, differences in atmospheric circulation patterns. The strongest volcanic signal (both in sulfate concentration and flux) was attributed to the AD 1452 Kuwae eruption, similar to the Plateau Remote and Talos Dome records. The average snow accumulation rate calculated between volcanic stratigraphic horizons for the period AD 1260–2010 is 20.9 mm H2O. Positive (+13%) anomalies of snow accumulation were found for AD 1661–1815 and AD 1992–2010, and negative (−12%) for AD 1260–1601. We hypothesized that the changes in snow accumulation are associated with regional peculiarities in atmospheric transport.

scholarly journals Enhanced moisture delivery into Victoria Land, East Antarctica, during the early Last Interglacial: implications for West Antarctic Ice Sheet stability

2021 ◽  
Vol 17 (5) ◽  
pp. 1841-1855
Author(s):  
Yuzhen Yan ◽  
Nicole E. Spaulding ◽  
Michael L. Bender ◽  
Edward J. Brook ◽  
John A. Higgins ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Ice Cores ◽  
Snow Accumulation ◽  
East Antarctica ◽  
Ice Age ◽  
Accumulation Rates ◽  
Last Interglacial ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Victoria Land

Abstract. The S27 ice core, drilled in the Allan Hills Blue Ice Area of East Antarctica, is located in southern Victoria Land, ∼80 km away from the present-day northern edge of the Ross Ice Shelf. Here, we utilize the reconstructed accumulation rate of S27 covering the Last Interglacial (LIG) period between 129 ka and 116 ka (where ka indicates thousands of years before present) to infer moisture transport into the region. The accumulation rate is based on the ice-age–gas-age differences calculated from the ice chronology, which is constrained by the stable water isotopes of the ice, and an improved gas chronology based on measurements of oxygen isotopes of O2 in the trapped gases. The peak accumulation rate in S27 occurred at 128.2 ka, near the peak LIG warming in Antarctica. Even the most conservative estimate yields an order-of-magnitude increase in the accumulation rate during the LIG maximum, whereas other Antarctic ice cores are typically characterized by a glacial–interglacial difference of a factor of 2 to 3. While part of the increase in S27 accumulation rates must originate from changes in the large-scale atmospheric circulation, additional mechanisms are needed to explain the large changes. We hypothesize that the exceptionally high snow accumulation recorded in S27 reflects open-ocean conditions in the Ross Sea, created by reduced sea ice extent and increased polynya size and perhaps by a southward retreat of the Ross Ice Shelf relative to its present-day position near the onset of the LIG. The proposed ice shelf retreat would also be compatible with a sea-level high stand around 129 ka significantly sourced from West Antarctica. The peak in S27 accumulation rates is transient, suggesting that if the Ross Ice Shelf had indeed retreated during the early LIG, it would have re-advanced by 125 ka.

scholarly journals Features of meteorological events preserved in a high-resolution Law Dome (East Antarctica) snow pit

2002 ◽  
Vol 35 ◽  
pp. 463-470 ◽  
Author(s):  
Alison J. McMorrow ◽  
Mark A. J. Curran ◽  
Tas D. Van Ommen ◽  
Vin I. Morgan ◽  
Ian Allison
Keyword(s):  
High Resolution ◽  
Austral Summer ◽  
Snow Accumulation ◽  
East Antarctica ◽  
Synoptic Scale ◽  
High Accumulation ◽  
Oxygen Isotope Ratios ◽  
Source Regions ◽  
Ion Species ◽  
Very High

AbstractSnow-pit and shallow firn-core records of oxygen isotope ratios (δ18O) and trace ion species were generated at a high-accumulation site on Law Dome, East Antarctica. Concordance between accumulation events identified in records up to 7.7 km a part confirms that the observed glaciochemical variations are the result of regional rather than local surface effects. This allows calibration of the snow-pit records with measured meteorological parameters. Net accumulation periods that comprise the snow-pit record are identified using hourly snow-accumulation measurements from a co-located automatic weather station (AWS). Particular focus is given to three net accumulation periods preserved during austral summer 1999/2000 that correspond to the top 0.5 m of the snow pit. Local meteorological conditions recorded during the summer accumulation periods by the AWS are combined with regional and synoptic-scale meteorology derived from Casey station (110 km away) and Advanced Very High Resolution Radiometer satellite imagery to identify potential source regions for chemical signals preserved in summer snow at Law Dome.

Sign in / Sign up

Export Citation Format

Share Document