scholarly journals Non-climatic signal in ice core records: lessons from Antarctic megadunes

2016 ◽  
Vol 10 (3) ◽  
pp. 1217-1227 ◽  
Author(s):  
Alexey Ekaykin ◽  
Lutz Eberlein ◽  
Vladimir Lipenkov ◽  
Sergey Popov ◽  
Mirko Scheinert ◽  
...  
Keyword(s):  
Spatial Variability ◽  
Isotopic Composition ◽  
Vertical Profile ◽  
Accumulation Rate ◽  
Climatic Variability ◽  
Ice Core ◽  
Ice Cores ◽  
Snow Accumulation ◽  
Vostok Station ◽  
Isotope Content

Abstract. We present the results of glaciological investigations in the megadune area located 30 km to the east of Vostok Station (central East Antarctica) implemented during the 58th, 59th and 60th Russian Antarctic Expedition (January 2013–2015). Snow accumulation rate and isotope content (δD, δ18O and δ17O) were measured along the 2 km profile across the megadune ridge accompanied by precise GPS altitude measurements and ground penetrating radar (GPR) survey. It is shown that the spatial variability of snow accumulation and isotope content covaries with the surface slope. The accumulation rate regularly changes by 1 order of magnitude within the distance < 1 km, with the reduced accumulation at the leeward slope of the dune and increased accumulation in the hollow between the dunes. At the same time, the accumulation rate averaged over the length of a dune wave (22 mm w.e.) corresponds well with the value obtained at Vostok Station, which suggests no additional wind-driven snow sublimation in the megadunes compared to the surrounding plateau. The snow isotopic composition is in negative correlation with the snow accumulation. Analysing dxs ∕ δD and 17O-excess ∕ δD slopes (where dxs  =  δD − 8 ⋅ δ18O and 17O-excess  =  ln(δ17O  ∕  1000 +  1) −0.528 ⋅ ln (δ18O ∕ 1000 + 1)), we conclude that the spatial variability of the snow isotopic composition in the megadune area could be explained by post-depositional snow modifications. Using the GPR data, we estimated the apparent dune drift velocity (4.6 ± 1.1 m yr−1). The full cycle of the dune drift is thus about 410 years. Since the spatial anomalies of snow accumulation and isotopic composition are supposed to drift with the dune, a core drilled in the megadune area would exhibit the non-climatic 410-year cycle of these two parameters. We simulated a vertical profile of snow isotopic composition with such a non-climatic variability, using the data on the dune size and velocity. This artificial profile is then compared with the real vertical profile of snow isotopic composition obtained from a core drilled in the megadune area. We note that the two profiles are very similar. The obtained results are discussed in terms of interpretation of data obtained from ice cores drilled beyond the megadune areas.

scholarly journals Non-climatic signal in ice core records: lessons from Antarctic mega-dunes

2015 ◽  
Vol 9 (6) ◽  
pp. 6909-6936
Author(s):  
A. Ekaykin ◽  
L. Eberlein ◽  
V. Lipenkov ◽  
S. Popov ◽  
M. Scheinert ◽  
...  
Keyword(s):  
Spatial Variability ◽  
Isotopic Composition ◽  
Vertical Profile ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Snow Accumulation ◽  
Vostok Station ◽  
Isotope Content ◽  
Dune Area

Abstract. We present the results of glaciological investigations in the mega-dune area located 30 km to the east from Vostok Station (central East Antarctica) implemented during the 58th, 59th and 60th Russian Antarctic Expedition (January 2013–January 2015). Snow accumulation rate and isotope content (δD, δ18O and δ17O) were measured along the 2 km profile across the mega-dune ridge accompanied by precise GPS altitude measurements and GPR survey. It is shown that the spatial variability of snow accumulation and isotope content covaries with the surface slope. The accumulation rate regularly changes by one order of magnitude within the distance < 1 km, with the reduced accumulation at the leeward slope of the dune and increased accumulation in the hollow between the dunes. At the same time, the accumulation rate averaged over the length of a dune wave (22 mm we) corresponds well with the value obtained at Vostok Station, which suggests no additional wind-driven snow sublimation in the mega-dunes compared to the surrounding plateau. The snow isotopic composition is in negative correlation with the snow accumulation. Analyzing dxs/δD and 17O-excess/δD slopes, we conclude that the spatial variability of the snow isotopic composition in the mega-dune area could be explained by post-depositional snow modifications. Using the GPR data, we estimated the apparent dune drift velocity (4.6 ± 1.1 m yr−1). The full cycle of the dune drift is thus about 410 years. Since the spatial anomalies of snow accumulation and isotopic composition are supposed to drift with the dune, an ice core drilled in the mega-dune area would exhibit the non-climatic 410 year cycle of these two parameters. We simulated a vertical profile of snow isotopic composition with such a non-climatic variability, using the data on the dune size and velocity. This artificial profile is then compared with the real vertical profile of snow isotopic composition obtained from a core drilled in the mega-dune area. We note that the two profiles are very similar. The obtained results are discussed in terms of interpretation of data obtained from ice cores drilled beyond the mega-dune areas.

Spatial variability of snow isotopic composition and accumulation rate at the stake farm of Vostok station (Сentral Antarctica)

2019 ◽  
Vol 65 (1) ◽  
pp. 46-62 ◽  
Author(s):  
A. A. Ekaykin ◽  
D. O. Vladimirova ◽  
N. A. Tebenkova ◽  
E. V. Brovkov ◽  
A. N. Veres ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Spatial Variability ◽  
Isotopic Composition ◽  
Accumulation Rate ◽  
Ice Sheet ◽  
Ice Cores ◽  
Snow Accumulation ◽  
Geochemical Data ◽  
Snow Surface ◽  
Vostok Station

The knowledge of the spatial distribution of the snow accumulation rate and isotopic composition in different scales, from local to continental, over the Antarctic Ice Sheet is critically important for the interpretation of the paleoclimate data obtained from deep ice cores, for correct assessment of the ice sheet mass balance, etc. With this in mind, we have synthesized geodetic, glaciological and geochemical data collected in the vicinity of central Antarctic Vostok station in 1970–2017 in order to shed light on the processes governing the spatial distribution of snow isotopic composition and accumulation rate in the spatial scale from 100 to 1000 m. First, we have discovered that snow surface height and snow accumulation rate field are strongly affected by the influence of the logistic convoy route annually operating between Russian Antarctic stations Vostok and Progress. This influence is detectable up to 1 km leeward from the route. At the same time the isotopic composition of the upper 10 cm of the snow does not show any anomalies in the vicinity of the route. This is an unexpected result, because large anomalies of the ice sheet surface (e.g., megadunes) are known to affect the snow isotopic composition. Second, in the undisturbed part of the snow surface near Vostok station we have discovered quasi-periodic (with the wavelength of about 400 m) low-amplitude variations of the surface height that are covariant with the corresponding waves in snow accumulation and isotopic composition. We suggest that spatial variability of the snow isotopic composition is due to the different ratio of summer and winter precipitation deposited in different locations, as evident from a strong negative correlation between δD and dxs parameters. The results of this study may explain the nature of the low-frequency noise (with the time-scale from decades to centuries) observed in the climate records obtained from shallow and deep ice cores in central Antarctica.

scholarly journals Large-scale drivers of Caucasus climate variability in meteorological records and Mt Elbrus ice cores

2016 ◽  
Author(s):  
Anna Kozachek ◽  
Vladimir Mikhalenko ◽  
Valérie Masson-Delmotte ◽  
Alexey Ekaykin ◽  
Patrick Ginot ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Large Scale ◽  
Isotope Composition ◽  
Accumulation Rate ◽  
Meteorological Data ◽  
Ice Core ◽  
Ice Cores ◽  
Snow Accumulation ◽  
The Caucasus ◽  
Precipitation Record

Abstract. A 181.2 m ice core was recovered from a borehole drilled into bedrock on the western plateau of Mt. Elbrus (43°20’53.9’’ N, 42°25’36.0’’ E; 5115 m a.s.l.) in the Caucasus, Russia, in 2009 (Mikhalenko et al., 2015). Here, we report on the results of the water stable isotope composition from this ice core in comparison with results from shallow ice cores. There is a distinct seasonal cycle of the isotopic composition which allowed dating by annual layer counting. Dating has been performed for the upper 126 m of the deep core combined with shallow cores data. The whole record covers one century from 2013 back to 1914. Due to the high accumulation rate (1380 mm w.e. per year) and limited melting we obtained the isotopic composition and accumulation rate records with seasonal resolution. These values were compared with available meteorological data from 13 weather stations in the region, and also with atmosphere circulation indices, back-trajectories calculations and GNIP data in order to decipher the drivers of accumulation and ice core isotopic composition in the Caucasus region. In the summer season the isotopic composition depends on the local temperature, while in winter, the atmospheric circulation is the predominant driver of the ice core isotopic composition. The snow accumulation rate correlates well with the precipitation rate in the region all year round, this made it possible to reconstruct and expand the precipitation record at the Caucasus highlands from 1914 till 1966 when the reliable meteorological observations of precipitation at high elevation began.

scholarly journals Large-scale drivers of Caucasus climate variability in meteorological records and Mt El'brus ice cores

2017 ◽  
Vol 13 (5) ◽  
pp. 473-489 ◽  
Author(s):  
Anna Kozachek ◽  
Vladimir Mikhalenko ◽  
Valérie Masson-Delmotte ◽  
Alexey Ekaykin ◽  
Patrick Ginot ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Isotope Composition ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Snow Accumulation ◽  
Global Network ◽  
Back Trajectory ◽  
The Caucasus ◽  
Precipitation Record

Abstract. A 181.8 m ice core was recovered from a borehole drilled into bedrock on the western plateau of Mt El'brus (43°20′53.9′′ N, 42°25′36.0′′ E; 5115 m a.s.l.) in the Caucasus, Russia, in 2009 (Mikhalenko et al., 2015). Here, we report on the results of the water stable isotope composition from this ice core with additional data from the shallow cores. The distinct seasonal cycle of the isotopic composition allows dating by annual layer counting. Dating has been performed for the upper 126 m of the deep core combined with 20 m from the shallow cores. The whole record covers 100 years, from 2013 back to 1914. Due to the high accumulation rate (1380 mm w.e. year−1) and limited melting, we obtained isotopic composition and accumulation rate records with seasonal resolution. These values were compared with available meteorological data from 13 weather stations in the region and also with atmosphere circulation indices, back-trajectory calculations, and Global Network of Isotopes in Precipitation (GNIP) data in order to decipher the drivers of accumulation and ice core isotopic composition in the Caucasus region. In the warm season (May–October) the isotopic composition depends on local temperatures, but the correlation is not persistent over time, while in the cold season (November–April), atmospheric circulation is the predominant driver of the ice core's isotopic composition. The snow accumulation rate correlates well with the precipitation rate in the region all year round, which made it possible to reconstruct and expand the precipitation record at the Caucasus highlands from 1914 until 1966, when reliable meteorological observations of precipitation at high elevation began.

scholarly journals Recent changes in north-west Greenland climate documented by NEEM shallow ice core data and simulations, and implications for past-temperature reconstructions

2015 ◽  
Vol 9 (4) ◽  
pp. 1481-1504 ◽  
Author(s):  
V. Masson-Delmotte ◽  
H. C. Steen-Larsen ◽  
P. Ortega ◽  
D. Swingedouw ◽  
T. Popp ◽  
...  
Keyword(s):  
19Th Century ◽  
North Atlantic ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Snow Accumulation ◽  
Last Interglacial ◽  
Bottom Part ◽  
Recent Climate ◽  
Temperature Reconstructions

Abstract. Combined records of snow accumulation rate, δ18O and deuterium excess were produced from several shallow ice cores and snow pits at NEEM (North Greenland Eemian Ice Drilling), covering the period from 1724 to 2007. They are used to investigate recent climate variability and characterise the isotope–temperature relationship. We find that NEEM records are only weakly affected by inter-annual changes in the North Atlantic Oscillation. Decadal δ18O and accumulation variability is related to North Atlantic sea surface temperature and is enhanced at the beginning of the 19th century. No long-term trend is observed in the accumulation record. By contrast, NEEM δ18O shows multidecadal increasing trends in the late 19th century and since the 1980s. The strongest annual positive δ18O values are recorded at NEEM in 1928 and 2010, while maximum accumulation occurs in 1933. The last decade is the most enriched in δ18O (warmest), while the 11-year periods with the strongest depletion (coldest) are depicted at NEEM in 1815–1825 and 1836–1846, which are also the driest 11-year periods. The NEEM accumulation and δ18O records are strongly correlated with outputs from atmospheric models, nudged to atmospheric reanalyses. Best performance is observed for ERA reanalyses. Gridded temperature reconstructions, instrumental data and model outputs at NEEM are used to estimate the multidecadal accumulation–temperature and δ18O–temperature relationships for the strong warming period in 1979–2007. The accumulation sensitivity to temperature is estimated at 11 ± 2 % °C−1 and the δ18O–temperature slope at 1.1 ± 0.2 ‰ °C−1, about twice as large as previously used to estimate last interglacial temperature change from the bottom part of the NEEM deep ice core.

scholarly journals Topographic control of regional accumulation rate variability at South Pole and implications for ice-core interpretation

2004 ◽  
Vol 39 ◽  
pp. 214-218 ◽  
Author(s):  
Gordon S. Hamilton
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Ice Sheet ◽  
Ice Cores ◽  
Snow Accumulation ◽  
Topographic Effects ◽  
South Pole ◽  
Accumulation Rates ◽  
Surface Slope ◽  
Ice Dynamics

AbstractSnow-accumulation rates are known to be sensitive to local changes in ice-sheet surface slope because of the effect of katabatic winds. These topographic effects can be preserved in ice cores that are collected at non-ice-divide locations. The trajectory of an ice-core site at South Pole is reconstructed using measurements of ice-sheet motion to show that snow was probably deposited at places of different surface slope during the past 1000 years. Recent accumulation rates, derived from shallow firn cores, vary along this trajectory according to surface topography, so that on a relatively steep flank mean annual accumulation is ∼18% smaller than on a nearby topographic depression. These modern accumulation rates are used to reinterpret the cause of accumulation rate variability with time in the long ice-core record as an ice-dynamics effect and not a climate-change signal. The results highlight the importance of conducting ancillary ice-dynamics measurements as part of ice-coring programs so that topographic effects can be deconvolved from potential climate signals.

scholarly journals The Chemical Stratigraphy of Polar Ice Sheets — A Method of Dating Ice Cores

1981 ◽  
Vol 27 (95) ◽  
pp. 3-9
Author(s):  
A. T. Wilson ◽  
C. H. Hendy
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Ice Sheet ◽  
Ice Cores ◽  
Antarctic Ice Sheet ◽  
The Core ◽  
Similar Work ◽  
Polar Ice Sheets ◽  
Vostok Station ◽  
East Antarctic Ice Sheet

AbstractStudies of the chemical stratigraphy in the snow near Vostok station, which is near the centre of the East Antarctic ice sheet, show that sodium exhibits annual concentration differences of up to a factor of ten. Similar work on the 952 m Vostok ice core enabled accumulation rates along selected parts of the core to be determined. This in turn enables the core to be dated. The accumulation rate in this central region of the East Antarctic ice sheet for the last 50000 years has been determined and is presented. An interesting result is that the accumulation rate during the last glacial period is only half that in post-glacial times. Results from the bottom of the core provide some evidence of a past surge in the East Antarctic ice sheet.

scholarly journals Deposition, recycling, and archival of nitrate stable isotopes between the air–snow interface: comparison between Dronning Maud Land and Dome C, Antarctica

2020 ◽  
Vol 20 (9) ◽  
pp. 5861-5885 ◽  
Author(s):  
V. Holly L. Winton ◽  
Alison Ming ◽  
Nicolas Caillon ◽  
Lisa Hauge ◽  
Anna E. Jones ◽  
...  
Keyword(s):  
Stable Isotopes ◽  
Uv Radiation ◽  
Mass Concentration ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Skin Layer ◽  
Snow Accumulation ◽  
Depth Profiles ◽  
Dronning Maud Land

Abstract. The nitrogen stable isotopic composition in nitrate (δ15N-NO3-) measured in ice cores from low-snow-accumulation regions in East Antarctica has the potential to provide constraints on past ultraviolet (UV) radiation and thereby total column ozone (TCO) due to the sensitivity of nitrate (NO3-) photolysis to UV radiation. However, understanding the transfer of reactive nitrogen at the air–snow interface in polar regions is paramount for the interpretation of ice core records of δ15N-NO3- and NO3- mass concentrations. As NO3- undergoes a number of post-depositional processes before it is archived in ice cores, site-specific observations of δ15N-NO3- and air–snow transfer modelling are necessary to understand and quantify the complex photochemical processes at play. As part of the Isotopic Constraints on Past Ozone Layer Thickness in Polar Ice (ISOL-ICE) project, we report new measurements of NO3- mass concentration and δ15N-NO3- in the atmosphere, skin layer (operationally defined as the top 5 mm of the snowpack), and snow pit depth profiles at Kohnen Station, Dronning Maud Land (DML), Antarctica. We compare the results to previous studies and new data, presented here, from Dome C on the East Antarctic Plateau. Additionally, we apply the conceptual 1D model of TRansfer of Atmospheric Nitrate Stable Isotopes To the Snow (TRANSITS) to assess the impact of NO3- recycling on δ15N-NO3- and NO3- mass concentrations archived in snow and firn. We find clear evidence of NO3- photolysis at DML and confirmation of previous theoretical, field, and laboratory studies that UV photolysis is driving NO3- recycling and redistribution at DML. Firstly, strong denitrification of the snowpack is observed through the δ15N-NO3- signature, which evolves from the enriched snowpack (−3 ‰ to 100 ‰), to the skin layer (−20 ‰ to 3 ‰), to the depleted atmosphere (−50 ‰ to −20 ‰), corresponding to mass loss of NO3- from the snowpack. Based on the TRANSITS model, we find that NO3- is recycled two times, on average, before it is archived in the snowpack below 15 cm and within 0.75 years (i.e. below the photic zone). Mean annual archived δ15N-NO3- and NO3- mass concentration values are 50 ‰ and 60 ng g−1, respectively, at the DML site. We report an e-folding depth (light attenuation) of 2–5 cm for the DML site, which is considerably lower than Dome C. A reduced photolytic loss of NO3- at DML results in less enrichment of δ15N-NO3- than at Dome C mainly due to the shallower e-folding depth but also due to the higher snow accumulation rate based on TRANSITS-modelled sensitivities. Even at a relatively low snow accumulation rate of 6 cm yr−1 (water equivalent; w.e.), the snow accumulation rate at DML is great enough to preserve the seasonal cycle of NO3- mass concentration and δ15N-NO3-, in contrast to Dome C where the depth profiles are smoothed due to longer exposure of surface snow layers to incoming UV radiation before burial. TRANSITS sensitivity analysis of δ15N-NO3- at DML highlights that the dominant factors controlling the archived δ15N-NO3- signature are the e-folding depth and snow accumulation rate, with a smaller role from changes in the snowfall timing and TCO. Mean TRANSITS model sensitivities of archived δ15N-NO3- at the DML site are 100 ‰ for an e-folding depth change of 8 cm, 110 ‰ for an annual snow accumulation rate change of 8.5 cm yr−1 w.e., 10 ‰ for a change in the dominant snow deposition season between winter and summer, and 10 ‰ for a TCO change of 100 DU (Dobson units). Here we set the framework for the interpretation of a 1000-year ice core record of δ15N-NO3- from DML. Ice core δ15N-NO3- records at DML will be less sensitive to changes in UV than at Dome C; however the higher snow accumulation rate and more accurate dating at DML allows for higher-resolution δ15N-NO3- records.

scholarly journals Spatial and temporal variability of snow accumulation in East Antarctica from traverse data

2005 ◽  
Vol 51 (172) ◽  
pp. 113-124 ◽  
Author(s):  
Massimo Frezzotti ◽  
Michel Pourchet ◽  
Onelio Flora ◽  
Stefano Gandolfi ◽  
Michel Gay ◽  
...  
Keyword(s):  
Spatial Variability ◽  
Temporal Variability ◽  
Accumulation Rate ◽  
Ice Core ◽  
Snow Accumulation ◽  
East Antarctica ◽  
Spatial And Temporal Variability ◽  
Volcanic Event ◽  
Terra Nova Bay ◽  
Order Of Magnitude

AbstractRecent snow accumulation rate is a key quantity for ice-core and mass-balance studies. Several accumulation measurement methods (stake farm, fin core, snow-radar profiling, surface morphology, remote sensing) were used, compared and integrated at eight sites along a transect from Terra Nova Bay to Dome C, East Antarctica, to provide information about the spatial and temporal variability of snow accumulation. Thirty-nine cores were dated by identifying tritium/b marker levels (1965_66) and non-sea-salt (nss) SO42_ spikes of the Tambora (Indonesia) volcanic event (1816) in order to provide information on temporal variability. Cores were linked by snow radar and global positioning system surveys to provide detailed information on spatial variability in snow accumulation. Stake-farm and ice-core accumulation rates are observed to differ significantly, but isochrones (snow radar) correlate well with ice-core derived accumulation. The accumulation/ablation pattern from stake measurements suggests that the annual local noise (metre scale) in snow accumulation can approach 2 years of ablation and more than four times the average annual accumulation, with no accumulation or ablation for a 5 year period in up to 40% of cases. The spatial variability of snow accumulation at the kilometre scale is one order of magnitude higher than temporal variability at the multi-decadal/secular scale. Stake measurements and firn cores at Dome C confirm an approximate 30% increase in accumulation over the last two centuries, with respect to the average over the last 5000 years

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.

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