The potential effects of percolating snowmelt on palynological records from firn and glacier ice

AbstractThe effects of meltwater percolation on pollen in snow, firn and glacial ice are not fully understood and currently hamper the use of pollen in ice-core studies of paleoclimate. Several studies have suggested that, due to grain size, pollen is not mobilized by meltwater transport. However, these findings contradict many ice-core pollen studies that show pollen concentrations in snow and firn are much higher than concentrations found in the ice layers they eventually form. This study addresses one aspect of this question by investigating whether meltwater percolation can effectively transport pollen within a snowpack. We used nine Styrofoam coolers filled by natural snow accumulation. The coolers were tested in three groups of three replicates each to simulate different glacier snowpack conditions, and spiked at the surface with a known amount of Lycopodium marker spores. The snow was melted to two-thirds the original volume, sampled stratigraphically and tested for spore concentrations. Meltwater effluent was also collected and examined. Results show substantial vertical and horizontal spore transport during the experiment. Peak spore concentrations were found in the bottommost snow layer or in the meltwater effluent in eight of nine coolers, indicating that the majority of surface spores were transported through the snowpack via meltwater percolation and/or runoff.

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Using a composite flow law to model deformation in the NEEM deep ice core, Greenland: Part 1 the role of grain size and grain size distribution on the deformation of Holocene and glacial ice

10.5194/tc-2018-274 ◽

2019 ◽

Author(s):

Ernst-Jan N. Kuiper ◽

Ilka Weikusat ◽

Johannes H. P. de Bresser ◽

Daniela Jansen ◽

Gill M. Pennock ◽

...

Keyword(s):

Grain Size ◽

Strain Rate ◽

Rheological Model ◽

Basal Slip ◽

Ice Core ◽

Glacial Ice ◽

Micro Scale ◽

Fine Grained ◽

Composite Flow ◽

End Members

Abstract. The effect of grain size on strain rate of ice in the upper 2207 m in the North Greenland Eemian Ice Drilling (NEEM) deep ice core was investigated using a rheological model based on the composite flow law of Goldsby and Kohlstedt (1997, 2001). The grain size was described by both a mean grain size and a grain size distribution, which allowed the strain rate to be calculated using two different model end members: (i) the micro-scale constant stress model where each grain deforms by the same stress and (ii) the micro-scale constant strain rate model where each grain deforms by the same strain rate. The model results show that basal slip accommodated by grain boundary sliding produces almost all of the deformation in the upper 2207 m of the NEEM ice core, while dislocation creep (basal slip accommodated by non-basal slip) hardly contributes to deformation. The difference in calculated strain rate between the two model end members is relatively small. The calculated strain rate in the fine grained glacial ice (1419–2207 m) varies strongly with depth and is about 4–5 times higher than in the coarser grained Holocene ice (0–1419 m). Two peaks in strain rate are predicted at about 1980 and 2100 m of depth. The results from the rheological model and microstructures in the glacial ice indicate that fine grained layers in the glacial ice will act as internal preferential sliding zones in the Greenland ice sheet.

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Using a composite flow law to model deformation in the NEEM deep ice core, Greenland – Part 1: The role of grain size and grain size distribution on deformation of the upper 2207 m

The Cryosphere ◽

10.5194/tc-14-2429-2020 ◽

2020 ◽

Vol 14 (7) ◽

pp. 2429-2448 ◽

Cited By ~ 3

Author(s):

Ernst-Jan N. Kuiper ◽

Ilka Weikusat ◽

Johannes H. P. de Bresser ◽

Daniela Jansen ◽

Gill M. Pennock ◽

...

Keyword(s):

Grain Size ◽

Strain Rate ◽

Size Distribution ◽

Ice Core ◽

Dislocation Creep ◽

Glacial Ice ◽

Fine Grained ◽

Composite Flow ◽

Flow Law ◽

End Members

Abstract. The effect of grain size on strain rate of ice in the upper 2207 m in the North Greenland Eemian Ice Drilling (NEEM) deep ice core was investigated using a rheological model based on the composite flow law of Goldsby and Kohlstedt (1997, 2001). The grain size was described by both a mean grain size and a grain size distribution, which allowed the strain rate to be calculated using two different model end-members: (i) the microscale constant stress model where each grain deforms by the same stress and (ii) the microscale constant strain rate model where each grain deforms by the same strain rate. The model results predict that grain-size-sensitive flow produces almost all of the deformation in the upper 2207 m of the NEEM ice core, while dislocation creep hardly contributes to deformation. The difference in calculated strain rate between the two model end-members is relatively small. The predicted strain rate in the fine-grained Glacial ice (that is, ice deposited during the last Glacial maximum at depths of 1419 to 2207 m) varies strongly within this depth range and, furthermore, is about 4–5 times higher than in the coarser-grained Holocene ice (0–1419 m). Two peaks in strain rate are predicted at about 1980 and 2100 m depth. The prediction that grain-size-sensitive creep is the fastest process is inconsistent with the microstructures in the Holocene age ice, indicating that the rate of dislocation creep is underestimated in the model. The occurrence of recrystallization processes in the polar ice that did not occur in the experiments may account for this discrepancy. The prediction of the composite flow law model is consistent with microstructures in the Glacial ice, suggesting that fine-grained layers in the Glacial ice may act as internal preferential sliding zones in the Greenland ice sheet.

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Using a composite flow law to model deformation in the NEEM deep ice core, Greenland: Part 2 the role of grain size and premelting on ice deformation at high homologous temperature

10.5194/tc-2018-275 ◽

2019 ◽

Author(s):

Ernst-Jan N. Kuiper ◽

Johannes H. P. de Bresser ◽

Martyn R. Drury ◽

Jan Eichler ◽

Gill M. Pennock ◽

...

Keyword(s):

Grain Size ◽

Basal Slip ◽

Ice Core ◽

Coarse Grained ◽

Strain Rates ◽

Glacial Ice ◽

Fine Grained ◽

Composite Flow ◽

Flow Law ◽

Limited Creep

Abstract. The ice microstructure in the lower part of the North Greenland Eemian Ice Drilling (NEEM) ice core consists of relatively fine grained glacial ice with a single maximum crystallographic preferred orientation (CPO) alternated by much coarser grained Eemian ice with a partial girdle type of CPO. In this study, the grain size sensitive (GSS) composite flow law of Goldsby and Kohlstedt (2001) was used to study the effects of grain size and premelting on strain rate in the lower part of the NEEM ice core. The results show that the strain rates predicted in the fine grained glacial layers are about an order of magnitude higher than in the much coarser grained Eemian layers. The dominant deformation mechanisms between the layers is also different with basal slip accommodated by grain boundary sliding (GBS-limited creep) being the dominant deformation mechanism in the glacial layers, while GBS-limited creep and dislocation creep (basal slip accommodated by non-basal slip) contribute both roughly equally to bulk strain in the coarse grained layers. Due to the large difference in microstructure between the impurity-rich glacial ice and the impurity-depleted Eemian ice at premelting temperatures (T>262 K), it is expected that the fine grained layers deform mainly by simple shear at high strain rates, while the coarse grained layers are relatively stagnant. The difference in microstructure, and consequently in viscosity, between glacial and interglacial ice at temperatures just below the melting point can have important consequences for ice dynamics close to the bedrock.

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Spatial pattern of accumulation at Taylor Dome during the last glacial inception: stratigraphic constraints from Taylor Glacier

10.5194/cp-2018-53 ◽

2018 ◽

Author(s):

James A. Menking ◽

Edward J. Brook ◽

Sarah A. Shackleton ◽

Jeffrey P. Severinghaus ◽

Michael Dyonisius ◽

...

Keyword(s):

Ice Core ◽

Snow Accumulation ◽

Ice Age ◽

Spatial Gradient ◽

Age Difference ◽

Last Glacial ◽

Accumulation Zone ◽

Glacier Ice ◽

Taylor Glacier ◽

The Last Glacial

Abstract. A new ice core retrieved from the Taylor Glacier blue ice area contains ice and air spanning the Marine Isotope Stage (MIS) 5/4 transition (74 to 65 ka), a period of global cooling and glacial inception. Dating the ice and air bubbles in the new ice core reveals an ice age-gas age difference (Δage) approaching 10 ka during MIS 4, implying very low accumulation at the Taylor Glacier accumulation zone on the northern flank of Taylor Dome. A revised chronology for the Taylor Dome ice core (80 to 55 ka), situated to the south of the Taylor Glacier accumulation zone, shows that Δage did not exceed 2.5 ka at that location. The difference in Δage between the new Taylor Glacier ice core and the Taylor Dome ice core implies a spatial gradient in snow accumulation across Taylor Dome that intensified during the last glacial inception and through MIS 4.

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Glacier ice archives nearly 15,000-year-old microbes and phages

Microbiome ◽

10.1186/s40168-021-01106-w ◽

2021 ◽

Vol 9 (1) ◽

Author(s):

Zhi-Ping Zhong ◽

Funing Tian ◽

Simon Roux ◽

M. Consuelo Gazitúa ◽

Natalie E. Solonenko ◽

...

Keyword(s):

Climate Change ◽

Ice Core ◽

Ice Cores ◽

Single Species ◽

Amplicon Sequencing ◽

Future Climate Change ◽

Climate Conditions ◽

Glacier Ice ◽

Sampling Procedures ◽

Functional Genome

Abstract Background Glacier ice archives information, including microbiology, that helps reveal paleoclimate histories and predict future climate change. Though glacier-ice microbes are studied using culture or amplicon approaches, more challenging metagenomic approaches, which provide access to functional, genome-resolved information and viruses, are under-utilized, partly due to low biomass and potential contamination. Results We expand existing clean sampling procedures using controlled artificial ice-core experiments and adapted previously established low-biomass metagenomic approaches to study glacier-ice viruses. Controlled sampling experiments drastically reduced mock contaminants including bacteria, viruses, and free DNA to background levels. Amplicon sequencing from eight depths of two Tibetan Plateau ice cores revealed common glacier-ice lineages including Janthinobacterium, Polaromonas, Herminiimonas, Flavobacterium, Sphingomonas, and Methylobacterium as the dominant genera, while microbial communities were significantly different between two ice cores, associating with different climate conditions during deposition. Separately, ~355- and ~14,400-year-old ice were subject to viral enrichment and low-input quantitative sequencing, yielding genomic sequences for 33 vOTUs. These were virtually all unique to this study, representing 28 novel genera and not a single species shared with 225 environmentally diverse viromes. Further, 42.4% of the vOTUs were identifiable temperate, which is significantly higher than that in gut, soil, and marine viromes, and indicates that temperate phages are possibly favored in glacier-ice environments before being frozen. In silico host predictions linked 18 vOTUs to co-occurring abundant bacteria (Methylobacterium, Sphingomonas, and Janthinobacterium), indicating that these phages infected ice-abundant bacterial groups before being archived. Functional genome annotation revealed four virus-encoded auxiliary metabolic genes, particularly two motility genes suggest viruses potentially facilitate nutrient acquisition for their hosts. Finally, given their possible importance to methane cycling in ice, we focused on Methylobacterium viruses by contextualizing our ice-observed viruses against 123 viromes and prophages extracted from 131 Methylobacterium genomes, revealing that the archived viruses might originate from soil or plants. Conclusions Together, these efforts further microbial and viral sampling procedures for glacier ice and provide a first window into viral communities and functions in ancient glacier environments. Such methods and datasets can potentially enable researchers to contextualize new discoveries and begin to incorporate glacier-ice microbes and their viruses relative to past and present climate change in geographically diverse regions globally.

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Evidence for a large surface ablation zone in central East Antarctica during the last Ice Age

Quaternary Research ◽

10.1016/s0033-5894(02)00014-5 ◽

2003 ◽

Vol 59 (1) ◽

pp. 114-121 ◽

Cited By ~ 26

Author(s):

Martin J. Siegert ◽

Richard C. A. Hindmarsh ◽

Gordon S. Hamilton

Keyword(s):

Ice Core ◽

Remote Sensing Data ◽

Ice Age ◽

Internal Layers ◽

Ice Flow ◽

Glacial Ice ◽

Ice Surface ◽

Ice Flows ◽

Last Ice Age ◽

The Hill

AbstractInternal isochronous ice sheet layers, recorded by airborne ice-penetrating radar, were measured along an ice flowline across a large (>1 km high) subglacial hill in the foreground of the Transantarctic Mountains. The layers, dated through an existing stratigraphic link with the Vostok ice core, converge with the ice surface as ice flows over the hill without noticeable change to their separation with each other or the ice base. A two-dimensional ice flow model that calculates isochrons and particle flowpaths and accounts for ice flow over the hill under steady-state conditions requires net ablation (via sublimation) over the stoss face for the predicted isochrons to match the measured internal layers. Satellite remote sensing data show no sign of exposed ancient ice at this site, however. Given the lack of exposed glacial ice, surface balance conditions must have changed recently from the net ablation that is predicted at this site for the last 85,000 years to accumulation.

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Spatial and temporal variability in isotope composition of recent snow in the vicinity of Vostok station, Antarctica: implications for ice-core record interpretation

Annals of Glaciology ◽

10.3189/172756402781816726 ◽

2002 ◽

Vol 35 ◽

pp. 181-186 ◽

Cited By ~ 74

Author(s):

Alexey A. Ekaykin ◽

Vladimir Ya. Lipenkov ◽

Narcisse I. Barkov ◽

Jean Robert Petit ◽

Valerie Masson-Delmotte

Keyword(s):

Isotope Composition ◽

Ice Core ◽

Snow Accumulation ◽

Spatial And Temporal Variability ◽

Weak Correlation ◽

Ice Core Record ◽

Vostok Station ◽

The Mean ◽

Mean Annual Air Temperature ◽

Snow Samples

AbstractContinuous, detailed isotope (δD and δ18O) profiles were obtained from eight snow pits dug in the vicinity of Vostok station, Antarctica, during the period 1984– 2000. In addition, snow samples taken along the 1km long accumulation-stake profile were measured to determine spatial variability in isotope composition of recent snow. the stacked δD time series spanning the last 55 years shows only weak correlation with the mean annual air temperature recorded at Vostok station. Significant oscillations of both snow accumulation and snow isotope composition with the periods 2.5, 5, 20 and, possibly, ~102 years observed at single points are interpreted in terms of drift of snow-accumulation waves of various scales on the surface of the ice sheet.

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Reconstructing Antarctic snow accumulation using nitrogen isotopes of nitrate

10.5194/egusphere-egu21-672 ◽

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

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 (d15N) 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 14NO3- over 15NO3-, and thus the d15N 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 d15N values. A linear relationship (r2 = 0.86) between d15N and net accumulation-1 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-2 yr-1 at deep interior sites to >400 kg m-2 yr-1 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.

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Melt regimes, stratigraphy, flow dynamics and glaciochemistry of three glaciers in the Alaska Range

Journal of Glaciology ◽

10.3189/2012jog10j238 ◽

2012 ◽

Vol 58 (207) ◽

pp. 99-109 ◽

Cited By ~ 9

Author(s):

Seth Campbell ◽

Karl Kreutz ◽

Erich Osterberg ◽

Steven Arcone ◽

Cameron Wake ◽

...

Keyword(s):

Ground Penetrating Radar ◽

Ice Core ◽

Chemical Diffusion ◽

Flow Dynamics ◽

Alaska Range ◽

Ice Volume ◽

Glacier Ice ◽

Age Model ◽

Ground Penetrating ◽

Climate Studies

AbstractWe used ground-penetrating radar (GPR), GPS and glaciochemistry to evaluate melt regimes and ice depths, important variables for mass-balance and ice-volume studies, of Upper Yentna Glacier, Upper Kahiltna Glacier and the Mount Hunter ice divide, Alaska. We show the wet, percolation and dry snow zones located below ~2700ma.s.l., at ~2700 to 3900ma.s.l. and above 3900ma.s.l., respectively. We successfully imaged glacier ice depths upwards of 480 m using 40-100 MHz GPR frequencies. This depth is nearly double previous depth measurements reached using mid-frequency GPR systems on temperate glaciers. Few Holocene-length climate records are available in Alaska, hence we also assess stratigraphy and flow dynamics at each study site as a potential ice-core location. Ice layers in shallow firn cores and attenuated glaciochemical signals or lacking strata in GPR profiles collected on Upper Yentna Glacier suggest that regions below 2800ma.s.l. are inappropriate for paleoclimate studies because of chemical diffusion, through melt. Flow complexities on Kahiltna Glacier preclude ice-core climate studies. Minimal signs of melt or deformation, and depth-age model estimates suggesting ~4815 years of ice on the Mount Hunter ice divide (3912ma.s.l.) make it a suitable Holocene-age ice-core location.

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Optical properties of ice and snow

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2018.0161 ◽

2019 ◽

Vol 377 (2146) ◽

pp. 20180161 ◽

Cited By ~ 19

Author(s):

Stephen G. Warren

Keyword(s):

Sea Ice ◽

Sheet Thickness ◽

Open Water ◽

Microwave Emission ◽

Radiative Properties ◽

Radio Waves ◽

Lake Ice ◽

Near Ultraviolet ◽

Glacier Ice ◽

Natural Snow

The interactions of electromagnetic radiation with ice, and with ice-containing media such as snow and clouds, are determined by the refractive index and absorption coefficient (the ‘optical constants’) of pure ice as functions of wavelength. Bulk reflectance, absorptance and transmittance are further influenced by grain size (for snow), bubbles (for glacier ice and lake ice) and brine inclusions (for sea ice). Radiative transfer models for clouds can also be applied to snow; the important differences in their radiative properties are that clouds are optically thinner and contain smaller ice crystals than snow. Absorption of visible and near-ultraviolet radiation by ice is so weak that absorption of sunlight at these wavelengths in natural snow is dominated by trace amounts of light-absorbing impurities such as dust and soot. In the thermal infrared, ice is moderately absorptive, so snow is nearly a blackbody, with emissivity 98–99%. The absorption spectrum of liquid water resembles that of ice from the ultraviolet to the mid-infrared. At longer wavelengths they diverge, so microwave emission can be used to detect snowmelt on ice sheets, and to discriminate between sea ice and open water, by remote sensing. Snow and ice are transparent to radio waves, so radar can be used to infer ice-sheet thickness.This article is part of the theme issue ‘The physics and chemistry of ice: scaffolding across scales, from the viability of life to the formation of planets’.

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