scholarly journals Warm-based basal sediment entrainment and far-field Pleistocene origin evidenced in central Transantarctic blue ice through stable isotopes and internal structures

2018 ◽  
Vol 64 (244) ◽  
pp. 185-196 ◽  
Author(s):  
JOSEPH A. GRALY ◽  
KATHY J. LICHT ◽  
CHRISTINE M. KASSAB ◽  
BROXTON W. BIRD ◽  
MICHAEL R. KAPLAN
Keyword(s):  
Stable Isotopes ◽  
Ice Core ◽  
Far Field ◽  
Ice Flow ◽  
Air Bubble ◽  
Internal Structures ◽  
Flow Speeds ◽  
Sediment Entrainment ◽  
Stable Isotopes Of Water ◽  
Basal Melting

ABSTRACTStable isotopes of water (δ18O and δ2H) were measured in the debris-laden ice underlying an Antarctic blue ice moraine, and in adjoining Law Glacier in the central Transantarctic Mountains. Air bubble content and morphology were assessed in shallow ice core samples. Stable isotope measurements plot either on the meteoric waterline or are enriched from it. The data cluster in two groups: the ice underlying the moraine has a δ2H:δ18O slope of 5.35 ± 0.92; ice from adjoining portions of Law Glacier has a slope of 6.69 ± 1.39. This enrichment pattern suggests the moraine's underlying blue ice entrained sediment through refreezing processes acting in an open system. Glaciological conditions favorable to warm-based sediment entrainment occur 30–50 km upstream. Basal melting and refreezing are further evidenced by abundant vapor figures formed from internal melting of the ice crystals. Both the moraine ice and Law Glacier are sufficiently depleted of heavy isotopes that their ice cannot be sourced locally, but instead must be derived from far-field interior regions of the higher polar plateau. Modeled ice flow speeds suggest the ice must be at least 80 ka old, with Law Glacier's ice possibly dating to OIS 5 and moraine ice older still.

scholarly journals Instruments and methods: a case study of ice core bubbles as strain indicators

2018 ◽  
Vol 60 (78) ◽  
pp. 8-19
Author(s):  
John M. Fegyveresi ◽  
Richard B. Alley ◽  
Donald E. Voigt ◽  
Joan J. Fitzpatrick ◽  
Lawrence A. Wilen
Keyword(s):  
Ice Core ◽  
Local Stress ◽  
Strain Gauges ◽  
Far Field ◽  
Ice Flow ◽  
Large Variability ◽  
Flow Deformation ◽  
Image Analyses ◽  
Local Stress Field

AbstractMeasurements of a sample from ~580 m depth in the WAIS Divide (WDC06A) ice core reveal that bubbles are preferentially elongated in the basal plane of their parent grain, as expected if bubble shape preserves the record of dominant basal glide. This suggests that a method using bubbles as strain gauges could provide insights to grain-scale ice deformation. We introduce a technique using fabric and image analyses of paired thin and thick sections. Comparison of the crystallographic orientations of 148 grains and the shape orientations of 2377 intragrain bubbles reveals a strongly preferred elongation of bubbles in the grain basal planes (R2 = 0.96). Elongation magnitudes are consistent with a balance between ice flow deformation and diffusive restoration, with larger bubbles more elongated. Assuming bubbles record ice strain, grains with greater resolved stress on their basal planes from the far-field ice flow stresses show greater deformation, but with large variability suggesting that heterogeneity of the local stress field causes deformation even in unfavorably oriented grains. A correlation is also observed among bubble elongation, grain size, and bubble size, explaining a small but significant fraction of the variance ( P< 0.05), with implications for controls on ice deformation, as discussed here.

scholarly journals Seasonal variations of snow chemistry at NEEM, Greenland

2011 ◽  
Vol 52 (58) ◽  
pp. 193-200 ◽  
Author(s):  
Takayuki Kuramoto ◽  
Kumiko Goto-Azuma ◽  
Motohiro Hirabayashi ◽  
Takayuki Miyake ◽  
Hideaki Motoyama ◽  
...  
Keyword(s):  
Stable Isotopes ◽  
Seasonal Variations ◽  
Ice Core ◽  
Late Summer ◽  
The Other ◽  
Late Winter ◽  
Surface Mass ◽  
Snow Chemistry ◽  
Double Peaks ◽  
Stable Isotopes Of Water

AbstarctWe conducted a pit study in July 2009 at the NEEM (North Greenland Eemian Ice Drilling) deep ice-coring site in northwest Greenland. To examine the seasonal variations of snow chemistry and characteristics of the drill site, we collected snow/firn samples from the wall of a 2 m deep pit at intervals of 0.03 m and analyzed them for electric conductivity, pH, Cl–, NO3–, SO42–, CH3SO3– (MSA), Na+, K+, Mg2+, Ca2+ and stable isotopes of water (δ18O and δD). Pronounced seasonal variations in the stable isotopes of water were observed, which indicated that the snow had accumulated regularly during the past 4 years. Concentrations of Na+, Cl– and Mg2+, which largely originate from sea salt, peaked in winter to early spring, while Ca2+, which mainly originates from mineral dust, peaked in late winter to spring, slightly later than Na+, Cl– and Mg2+. Concentrations of NO3– showed double peaks, one in summer and the other in winter to spring, whereas those of SO42– peaked in winter to spring. The winter-to-spring concentrations of NO3– and SO42– seem to have been strongly influenced by anthropogenic inputs. Concentrations of MSA showed double peaks, one in spring and the other in late summer to autumn. Our study confirms that the NEEM deep ice core can be absolutely dated to a certain depth by counting annual layers, using the seasonal variations of stable isotopes of water and those of ions. We calculated the annual surface mass balance for the years 2006–08. The mean annual balance was 176 mm w.e., and the balances for winter-to-summer and summer-to-winter halves of the year were 98 and 78 mm, respectively. Snow deposition during the winter-to-summer half of the year was greater than that during the summer-to-winter half by 10–20mm for all three years covered by this study.

scholarly journals Reconstruction of three centuries of annual accumulation rates based on the record of stable isotopes of water from Lomonosovfonna, Svalbard

2002 ◽  
Vol 35 ◽  
pp. 57-62 ◽  
Author(s):  
Veijo A. Pohjola ◽  
Tõnu A. Martma ◽  
Harro A. J. Meijer ◽  
John C. Moore ◽  
Elisabeth Isaksson ◽  
...  
Keyword(s):  
Stable Isotopes ◽  
Flow Model ◽  
Accumulation Rate ◽  
Ice Core ◽  
Accumulation Rates ◽  
Annual Cycles ◽  
Core Site ◽  
Ice Core Record ◽  
Stable Isotopes Of Water ◽  
Low Amplitude

AbstractWe use the upper 81 mof the record of stable isotopes of water from a 122m long ice core from Lomonosovfonna, central Spitsbergen, Svalbard, to construct an ice-core chronology and the annual accumulation rates over the icefield. the isotope cycles are counted in the ice-core record using a model that neglects short-wavelength and low-amplitude cycles. We find approximately the same number of δ18O cycles as years between known reference horizons, and assume these cycles represent annual cycles. Testing the validity of this assumption using cycles in δD shows that both records give similar numbers of cycles. Using the δ18O chronology, and decompressing the accumulation records using the Nye flow model, we calculate the annual accumulation for the ice-core site back to AD 1715. We find that the average accumulation rate from 1715 to 1950 was on average 0.30 mw.e. Accumulation rates increased about 25% during the later part of the 20th century to an average of 0.41 mw.e. for the period 1950–97. the accumulation rates show highly significant 2.1 and 21 year periodicities, which gives credibility to our time-scale.

scholarly journals Site information and initial results from deep ice drilling on Law Dome, Antarctica

1997 ◽  
Vol 43 (143) ◽  
pp. 3-10 ◽  
Author(s):  
V.I. Morgan ◽  
C.W. Wookey ◽  
J. Li ◽  
T.D. van Ommen ◽  
W. Skinner ◽  
...  
Keyword(s):  
Ice Core ◽  
Ice Sheet ◽  
High Accumulation ◽  
Ice Flow ◽  
Ice Cap ◽  
Basal Ice ◽  
Inland Ice ◽  
The Last Glacial Maximum ◽  
Initial Results ◽  
The Last Glacial

AbstractThe aim of deep ice drilling on Law Dome, Antarctica, has been to exploit the special characteristics of Law Dome summit, i.e. low temperature and high accumulation near an ice divide, to obtain a high-resolution ice core for climatic/environmental studies of the Holocene and the Last Glacial Maximum (LGM). Drilling was completed in February 1993, when basal ice containing small fragments of rock was reached at a depth of 1196 m. Accurate ice dating, obtained by counting annual layers revealed by fine-detail δ18О, peroxide and electrical-conductivity measurements, is continuous down to 399 m, corresponding to a date of AD 1304. Sulphate concentration measurements, made around depths where conductivity tracing indicates volcanic fallout, allow confirmation of the dating (for Agung in 1963 and Tambora in 1815) or estimates of the eruption date from the ice dating (for the Kuwae, Vanuatu, eruption ~1457). The lower part of the core is dated by extrapolating the layer-counting using a simple model of the ice flow. At the LGM, ice-fabric measurements show a large decrease (250 to 14 mm2) in crystal size and a narrow maximum in c-axis vertically. The main zone of strong single-pole fabrics however, is located higher up in a broad zone around 900 m. Oxygen-isotope (δ18O) measurements show Holocene ice down to 1113 m, the LGM at 1133 m and warm (δ18O) about the same as Holocene) ice near the base of the ice sheet. The LGM/Holocene δ18O shift of 7.0‰, only ~1‰ larger than for Vostok, indicates that Law Dome remained an independent ice cap and was not overridden by the inland ice sheet in the Glacial.

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

2003 ◽  
Vol 59 (1) ◽  
pp. 114-121 ◽  
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.

scholarly journals Nonequilibrium air clathrate hydrates in Antarctic ice: a paleopiezomdter for polar ice caps

1993 ◽  
Vol 90 (23) ◽  
pp. 11416-11418 ◽  
Author(s):  
H Craig ◽  
H Shoji ◽  
C C Langway
Keyword(s):  
Phase Boundary ◽  
Numerical Models ◽  
Equilibrium Phase ◽  
Vertical Displacement ◽  
Polar Ice ◽  
Ice Flow ◽  
Air Bubble ◽  
Ice Caps ◽  
General Parameter ◽  
Approximate Composition

"Craigite," the mixed-air clathrate hydrate found in polar ice caps below the depth of air-bubble stability, is a clathrate mixed crystal of approximate composition (N2O2).6H2O. Recent observations on the Byrd Station Antarctic core show that the air hydrate is present at a depth of 727 m, well above the predicted depth for the onset of hydrate stability. We propose that the air hydrate occurs some 100 m above the equilibrium phase boundary at Byrd Station because of "piezometry"--i.e., that the anomalous depth of hydrate occurrence is a relic of a previous greater equilibrium depth along the flow trajectory, followed by vertical advection of ice through the local phase-boundary depth. Flowline trajectories in the ice based on numerical models show that the required vertical displacement does indeed occur just upstream of Byrd Station. Air-hydrate piezometry can thus be used as a general parameter to study the details of ice flow in polar ice caps and the metastable persistence of the clathrate phase in regions of upwelling blue ice.

scholarly journals At what depth is the Eemian layer expected to be found at NEEM?

2008 ◽  
Vol 48 ◽  
pp. 100-102 ◽  
Author(s):  
Susanne L. Buchardt ◽  
Dorthe Dahl-Jensen
Keyword(s):  
Flow Model ◽  
Accumulation Rate ◽  
Ice Core ◽  
Monte Carlo Analysis ◽  
Interglacial Period ◽  
Ice Flow ◽  
North West ◽  
Flow Parameters ◽  
Drill Site ◽  
Radio Echo Sounding

AbstractNo continuous record from Greenland of the Eemian interglacial period (130–115 ka BP) currently exists. However, a new ice-core drill site has been suggested at 77.449˚ N, 51.056˚Win north-west Greenland (North Eemian or NEEM). Radio-echo sounding images and flow model investigations indicate that an undisturbed Eemian record may be obtained at NEEM. In this work, a two-dimensional ice flow model with time-dependent accumulation rate and ice thickness is used to estimate the location of the Eemian layer at the new drill site. The model is used to simulate the ice flow along the ice ridge leading to the drill site. Unknown flow parameters are found through a Monte Carlo analysis of the flow model constrained by observed isochrones in the ice. The results indicate that the Eemian layer is approximately 60m thick and that its base is located approximately 100m above bedrock.

scholarly journals Ice genesis and its long-term dynamics in Scărişoara Ice Cave, Romania

2010 ◽  
Vol 4 (4) ◽  
pp. 1909-1929
Author(s):  
A. Perşoiu ◽  
A. Pazdur
Keyword(s):  
Radiocarbon Dating ◽  
Ice Age ◽  
Clear Understanding ◽  
Lake Ice ◽  
Ice Flow ◽  
Paleoclimatic Significance ◽  
Basal Melting ◽  
Perennial Ice ◽  
Level Monitoring

Abstract. The paleoclimatic significance of the perennial ice deposit in Scărişoara Ice Cave has been remarked since the early 20th century, but a clear understanding of the processes involved in the genesis, age and long-term dynamics of ice hampered all attempts to extract valuable data on past climate and vegetation changes. In this paper, we present a model of ice genesis and dynamics, based on stable isotopes, ice level monitoring (modern and archived) and radiocarbon dating of organic matter found in the ice. Ice in Scărişoara Ice Cave mostly consists of layers of lake ice, produced as liquid water freezes from top to bottom in mid-autumn, a mechanism that was also acting in the past, during the Medieval Warm Period and the Little Ice Age. The ice block is not stable in shape and volume, being continuously modified by ablation on top, basal melting and lateral flow. Radiocarbon dating shows that the ice block is older than 1200 years, the rate of ice flow and basal melting suggesting that the ice could be much older.

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