scholarly journals Extreme snow metamorphism in the Allan Hills, Antarctica, as an analogue for glacial conditions with implications for stable isotope composition

2015 ◽  
Vol 61 (230) ◽  
pp. 1171-1182 ◽  
Author(s):  
Ruzica Dadic ◽  
Martin Schneebeli ◽  
Nancy A.N. Bertler ◽  
Margit Schwikowski ◽  
Margret Matzl
Keyword(s):  
Stable Isotope ◽  
Isotope Composition ◽  
Ice Core ◽  
Initial Density ◽  
Stratigraphic Sequence ◽  
The Core ◽  
Depositional Processes ◽  
Alternating Temperature ◽  
Glacial Periods ◽  
Ice Core Records

AbstractUnderstanding physical processes in near-zero accumulation areas can help us to better understand polar ice-core records, particularly during periods when accumulation rates were lower than today. We report measurements from a 5 m firn core from the Allan Hills, Antarctica, which include physical properties using computer tomography, stable isotope ratios δD and δ18O, and 210Pb activity. The core shows a highly metamorphosed firn with homogeneous and stable structure, but with discrete layers near the surface. The observed firn structure is caused by a combination of unique depositional and post-depositional processes. The irregular δD and δ18O signal does not follow the stratigraphic sequence and implies post-depositional modification caused by microscopic pressure gradients in the firn that can result from either forced ventilation over rough surfaces in the presence of wind or alternating temperature-gradients between the firn and the atmosphere. Our results also indicate impact snow deposition under high winds and with a high initial density and air exchange between the atmosphere and the snowpack.210Pb activity below 0.3 m falls below the detection limit, implying that most of the core is more than 100 years old. We conclude that the Allan Hills record provides a unique opportunity to investigate important processes that would have affected ice-core records from glacial periods.

scholarly journals Isotopic diffusion in polycrystalline ice

2003 ◽  
Vol 49 (166) ◽  
pp. 397-406 ◽  
Author(s):  
Alan W. Rempel ◽  
J. S. Wettlaufer
Keyword(s):  
Stable Isotopes ◽  
Stable Isotope ◽  
Vapor Phase ◽  
High Frequency ◽  
Ice Core ◽  
Accurate Analysis ◽  
Depositional Processes ◽  
Polycrystalline Ice ◽  
End Members

AbstractQuantitative ice-core paleoclimatology must account for post-depositional processes, such as vapor-phase diffusion in the firn. After pore close-off, diffusion continues to smooth the stable-isotope records δ18O and δD that are eventually recovered from the ice, leading to the loss of high-frequency information. Johnsen and others (1997) found much higher rates of diffusive smoothing in the Greenland Icecore Project (GRIP) Holocene ice than would be predicted by diffusion through solid ice alone, and Nye (1998) argued that transport through liquid veins might explain this apparent excess diffusion. However, the analysis of Johnsen and others (2000) indicates that the required vein dimensions may be unrealistically large. Here, we model the diffusion of stable isotopes in polycrystalline ice and show that the predictions of Nye (1998) and those of Johnsen and others (2000) actually represent two end-members in a range of potential behavior. Our model determines which of these asymptotic regimes more closely resembles the prevailing conditions and quantifies the role of pre-melted liquid in the smoothing of isotopic signals. The procedure thereby ties together the two approaches and provides a rostrum for accurate analysis of isotope records and paleotemperature reconstructions.

scholarly journals A Flow Model and a Time Scale for the Ice Core from Camp Century, Greenland

1969 ◽  
Vol 8 (53) ◽  
pp. 215-223 ◽  
Author(s):  
W. Dansgaard ◽  
S. J. Johnsen
Keyword(s):  
Steady State ◽  
Stable Isotope ◽  
Time Scale ◽  
Flow Model ◽  
Ice Core ◽  
Climatic Changes ◽  
Horizontal Velocity ◽  
Measured Temperature ◽  
The Core ◽  
Vertical Strain

A flow model is described for the Camp Century area in Greenland. The horizontal velocity profile along the core is assumed to be uniform from the surface down to y = 400 m above the bottom. Below this level, the horizontal velocity vx, is assumed to decrease proportionally to y. Furthermore, at a given y, vx is assumed to be proportional to the distance x from the ice divide. The resulting vertical strain-rate under steady-state conditions gives the age of the ice as a function of y. The flow model has explained the measured temperature profile, and the time scale has been verified by comparison between observed stable isotope variations and past climatic changes (at least 70 000 years back in time) estimated by other methods.

scholarly journals Pleistocene ice at the bottom of the Vavilov ice cap, Severnaya Zemlya, Russian Arctic

1996 ◽  
Vol 42 (142) ◽  
pp. 403-406 ◽  
Author(s):  
Michel Stiévenard ◽  
Vladimir Nikolaëv ◽  
Dmitri Yu Bol’shiyanov ◽  
Christine Fléhoc ◽  
Jean Jouzel ◽  
...  
Keyword(s):  
Stable Isotope ◽  
Isotope Composition ◽  
Russian Arctic ◽  
Stable Isotope Composition ◽  
The Core ◽  
Ice Cap ◽  
Basal Ice ◽  
Glacier Ice ◽  
Severnaya Zemlya ◽  
First Time

AbstractThe Vavilov ice cap was perforated in 1988 by a drilling which reached the underlying frozen sediments. In contrast to the overlying glacier ice, the basal ice is composed of different ice layers with a variable debris load. The stable-isotope composition of these layers shows δ values much lower than everywhere else in the core or in the Vavilov ice cap. This is most probably the signature of a remnant of Pleistocene ice which, for the first time, is shown to occur in the Russian Arctic.

Climatic imprint in the mechanical properties of ice sheets and its effect on ice flow: Observations from South Pole and EPICA Dome C ice cores

2020 ◽  
Author(s):  
Carlos Martin ◽  
Howard Conway ◽  
Michelle Koutnik ◽  
Catherine Ritz ◽  
Thomas Bauska ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Crystal Orientation ◽  
Ice Core ◽  
Ice Sheets ◽  
Ice Cores ◽  
South Pole ◽  
Ice Flow ◽  
Phase Sensitive ◽  
Glacial Periods ◽  
Ice Core Records

<p>The climatic conditions over ice sheets at the time of snow deposition and compaction imprint distinctive crystallographic properties to the resulting ice. As the snow gets buried, its macroscopic structure evolves due to vertical compression but retains traces of the climatic imprint that generate distinctive mechanical, thermal and optical properties. Because climate alternates between glaciar periods, that are colder and dustier, and interglacial periods, the ice sheets are composed from layers with alternating mechanical properties. Here we compare ice core dust content and crystal orientation fabrics, from the ice core records, with englacial vertical strain-rates, measured with a phase-sensitive radar (ApRES), at South Pole and EPICA Dome C ice cores. Similarly to previous observations, we show that ice deposited during glacial periods develops stronger crystal orientation fabrics. In addition, we show that ice deposited during glacial periods is harder to vertically compress and horizontally extend, up to about 3 times, but softer to shear. These variations in mechanical properties are typically ignored in ice-flow modelling but they could be critical to interpret ice core records. Also, we show that the changes in crystal orientation fabrics due to transitions from interglacial to glacial conditions can be detected by phase-sensitive radar. This information can be used to constrain age-depth in future ice-core locations.</p>

scholarly journals Pleistocene ice at the bottom of the Vavilov ice cap, Severnaya Zemlya, Russian Arctic

1996 ◽  
Vol 42 (142) ◽  
pp. 403-406 ◽  
Author(s):  
Michel Stiévenard ◽  
Vladimir Nikolaëv ◽  
Dmitri Yu Bol’shiyanov ◽  
Christine Fléhoc ◽  
Jean Jouzel ◽  
...  
Keyword(s):  
Stable Isotope ◽  
Isotope Composition ◽  
Russian Arctic ◽  
Stable Isotope Composition ◽  
The Core ◽  
Ice Cap ◽  
Basal Ice ◽  
Glacier Ice ◽  
Severnaya Zemlya ◽  
First Time

AbstractThe Vavilov ice cap was perforated in 1988 by a drilling which reached the underlying frozen sediments. In contrast to the overlying glacier ice, the basal ice is composed of different ice layers with a variable debris load. The stable-isotope composition of these layers shows δ values much lower than everywhere else in the core or in the Vavilov ice cap. This is most probably the signature of a remnant of Pleistocene ice which, for the first time, is shown to occur in the Russian Arctic.

scholarly journals Unexpected increase in elemental carbon values over the last 30 years observed in a Svalbard ice core

2014 ◽  
Vol 14 (9) ◽  
pp. 13197-13231
Author(s):  
M. M. Ruppel ◽  
E. Isaksson ◽  
J. Ström ◽  
E. Beaudon ◽  
J. Svensson ◽  
...  
Keyword(s):  
Elemental Carbon ◽  
Ice Core ◽  
Ice Cores ◽  
The Arctic ◽  
Radiative Energy ◽  
Atmospheric Measurements ◽  
The Past ◽  
Depositional Processes ◽  
Quartz Fibre ◽  
Ice Core Records

Abstract. Black carbon (BC) is a light-absorbing particle that warms the atmosphere–Earth system. The climate effects of BC are amplified in the Arctic where its deposition on light surfaces decreases the albedo and causes earlier melt of snow and ice. Despite its suggested significant role in Arctic climate warming there is little information on BC concentrations and deposition in the past. Here we present results on BC (here operationally defined as elemental carbon (EC)) concentrations and deposition on a Svalbard glacier between 1700 and 2004. The inner part of a 125 m deep ice core from Holtedahlfonna glacier (79°8' N, 13°16' E, 1150 m a.s.l.) was melted, filtered through a quartz fibre filter and analysed for EC using a thermal optical method. The EC values started to increase after 1850 and peaked around 1910, similar to ice core records from Greenland. Strikingly, the EC values again increase rapidly between 1970 and 2004. This rise is not seen in Greenland ice cores and it seems to contradict atmospheric BC measurements indicating generally decreasing atmospheric BC concentrations since 1989 in the Arctic. Several hypotheses, such as changes in scavenging efficiencies, post-depositional processes and differences in the vertical distribution of BC in the atmosphere, are discussed for the differences between the Svalbard and Greenland ice core records, and the ice core and atmospheric measurements in Svalbard. In addition, the divergent BC trends between Greenland and Svalbard ice cores may be caused by differences in the analytical methods used, including the operational definitions of quantified particles, and detection efficiencies of different-sized BC particles. Regardless of the cause of the increasing EC values in the recent decades, the results have significant implications for the past radiative energy balance at the coring site.

scholarly journals Increase in elemental carbon values between 1970 and 2004 observed in a 300-year ice core from Holtedahlfonna (Svalbard)

2014 ◽  
Vol 14 (20) ◽  
pp. 11447-11460 ◽  
Author(s):  
M. M. Ruppel ◽  
E. Isaksson ◽  
J. Ström ◽  
E. Beaudon ◽  
J. Svensson ◽  
...  
Keyword(s):  
Elemental Carbon ◽  
Ice Core ◽  
Ice Cores ◽  
The Arctic ◽  
Radiative Energy ◽  
Atmospheric Measurements ◽  
The Past ◽  
Depositional Processes ◽  
Quartz Fibre ◽  
Ice Core Records

Abstract. Black carbon (BC) is a light-absorbing particle that warms the atmosphere–Earth system. The climate effects of BC are amplified in the Arctic, where its deposition on light surfaces decreases the albedo and causes earlier melt of snow and ice. Despite its suggested significant role in Arctic climate warming, there is little information on BC concentrations and deposition in the past. Here we present results on BC (here operationally defined as elemental carbon (EC)) concentrations and deposition on a Svalbard glacier between 1700 and 2004. The inner part of a 125 m deep ice core from Holtedahlfonna glacier (79°8' N, 13°16' E, 1150 m a.s.l.) was melted, filtered through a quartz fibre filter and analysed for EC using a thermal–optical method. The EC values started to increase after 1850 and peaked around 1910, similar to ice core records from Greenland. Strikingly, the EC values again increase rapidly between 1970 and 2004 after a temporary low point around 1970, reaching unprecedented values in the 1990s. This rise is not seen in Greenland ice cores, and it seems to contradict atmospheric BC measurements indicating generally decreasing atmospheric BC concentrations since 1989 in the Arctic. For example, changes in scavenging efficiencies, post-depositional processes and differences in the vertical distribution of BC in the atmosphere are discussed for the differences between the Svalbard and Greenland ice core records, as well as the ice core and atmospheric measurements in Svalbard. In addition, the divergent BC trends between Greenland and Svalbard ice cores may be caused by differences in the analytical methods used, including the operational definitions of quantified particles, and detection efficiencies of different-sized BC particles. Regardless of the cause of the increasing EC values between 1970 and 2004, the results have significant implications for the past radiative energy balance at the coring site.

scholarly journals A Flow Model and a Time Scale for the Ice Core from Camp Century, Greenland

1969 ◽  
Vol 8 (53) ◽  
pp. 215-223 ◽  
Author(s):  
W. Dansgaard ◽  
S. J. Johnsen
Keyword(s):  
Steady State ◽  
Stable Isotope ◽  
Time Scale ◽  
Flow Model ◽  
Ice Core ◽  
Climatic Changes ◽  
Horizontal Velocity ◽  
Measured Temperature ◽  
The Core ◽  
Vertical Strain

A flow model is described for the Camp Century area in Greenland. The horizontal velocity profile along the core is assumed to be uniform from the surface down to y = 400 m above the bottom. Below this level, the horizontal velocity v x , is assumed to decrease proportionally to y. Furthermore, at a given y, v x is assumed to be proportional to the distance x from the ice divide. The resulting vertical strain-rate under steady-state conditions gives the age of the ice as a function of y. The flow model has explained the measured temperature profile, and the time scale has been verified by comparison between observed stable isotope variations and past climatic changes (at least 70 000 years back in time) estimated by other methods.

scholarly journals Accumulation variability over a small area in east Dronning Maud Land, Antarctica, as determined from shallow firn cores and snow pits: some implications for ice-core records

2005 ◽  
Vol 51 (174) ◽  
pp. 343-352 ◽  
Author(s):  
Lars Karlöf ◽  
Elisabeth Isaksson ◽  
Jan-Gunnar Winther ◽  
Niels Gundestrup ◽  
Harro A.J. Meijer ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Snow Accumulation ◽  
Accumulation Rates ◽  
Spatial Variance ◽  
Depositional Processes ◽  
Dronning Maud Land ◽  
Simple Statistical Analysis ◽  
Firn Core ◽  
Ice Core Records

AbstractWe investigate and quantify the variability of snow accumulation rate around a medium-depth firn core (160 m) drilled in east Dronning Maud Land, Antarctica (75°00′ S, 15°00’ E; 3470 m h.a.e. (ellipsoidal height)). We present accumulation data from five snow pits and five shallow (20 m) firn cores distributed within a 3.5–7 km distance, retrieved during the 2000/01 Nordic EPICA (European Project for Ice Coring in Antarctica) traverse. Snow accumulation rates estimated for shorter periods show higher spatial variance than for longer periods. Accumulation variability as recorded from the firn cores and snow pits cannot explain all the variation in the ion and isotope time series; other depositional and post-depositional processes need to be accounted for. Through simple statistical analysis we show that there are differences in sensitivity to these processes between the analyzed species. Oxygen isotopes and sulphate are more conservative in their post-depositional behaviour than the more volatile acids, such as nitrate and to some degree chloride and methanesulphonic acid. We discuss the possible causes for the accumulation variability and the implications for the interpretation of ice-core records.

scholarly journals Weighting alternative for water stable isotopes: Statical comparison between station- and firn/ice-records

2017 ◽  
Vol 38 (2) ◽  
pp. 105-124
Author(s):  
István Gábor Hatvani ◽  
Zoltán Kern
Keyword(s):  
Stable Isotope ◽  
Air Temperature ◽  
Ice Core ◽  
Precipitation Amount ◽  
Ice Cores ◽  
Arithmetic Means ◽  
Depositional Processes ◽  
Water Stable Isotope ◽  
Annual Water ◽  
Water Isotope

Abstract It is generally accepted that ice cores archive amount-weighted water stable isotope signals. In order to achieve an improved understanding of the nature of water stable isotope signals stored in ice cores annual δ18O and δ2H averages (i.e. amount-weighted) were calculated for two Antarctic meteorological stations, Vernadsky and Hal­ley Bay, using monthly precipitation amount and monthly net accumulation as weights, respectively. These were then compared with the annual mean δ18O δ2H and records of the nearest available ice cores. In addition, at the stations, both arithmetic means (i.e. time-weighted) and amount-weighted (precipitation amount and net accumulation used as weights) annual air temperature averages were calculated and then compared to amount weighted annual mean δ18O and δ2H using correlation- and regression analyses. The main hypothesis was that amount weighted annual mean water isotope and temperature records from the stations would be able to replicate the annual water isotope signal stored in ice cores to a higher degree. Results showed that (i) amount weighting is incapable of ameliorating the signal replication between the stations and the ice cores, while arithmetic means gave the stronger linear relationships; (ii) post depositional processes may have a more determining effect on the isotopic composition of the firn than expected; and (iii) mean annual air temperature provided the closest match to ice core derived annual water isotope records. This latter conveys a similar message to that of recent findings, in as much as ambient temperature, via equilibrium isotope fractionation, is imprinted into the uppermost snow layer by vapor exchange even between precipitation events. Together, these observations imply that ice core stable water isotope records can be a more continuous archive of near-surface temperature changes than hitherto believed.

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